The U.S. promised "appropriate action" Friday in response to its assessment that an Iranian missile was responsible for downing a Ukrainian jetliner that crashed outside Tehran, as the Iranian government denied playing a role in the killing of all 176 people on board.

Secretary of State Mike Pompeo became the highest-level U.S. official to directly pin the blame on Iran, after Canadian, Australian and British leaders announced similar intelligence conclusions Thursday. "We do believe it is likely that that plane was shot down by an Iranian missile," he said.

Pompeo said an investigation would continue into the incident and that once it was complete he was "confident that we and the world will take appropriate action as a response." Leaders said the plane appeared to have been unintentionally hit by a surface-to-air missile.

Earlier Friday, Iran denied Western allegations that one of its own missiles downed the jetliner that crashed early Wednesday outside Tehran, hours after Iran launched more than a dozen ballistic missiles at two U.S. bases in Iraq to avenge the killing of its top general in an American airstrike last week.

"What is obvious for us, and what we can say with certainty, is that no missile hit the plane," Ali Abedzadeh, head of Iran's national aviation department, told a press conference.

"If they are really sure, they should come and show their findings to the world" in accordance with international standards, he added.

Hassan Rezaeifar, the head of the Iranian investigation team, said recovering data from the black box flight recorders could take more than a month and that the entire investigation could stretch into next year. He also said Iran may request help from international experts if it is not able to extract the flight recordings.

The ballistic missile attack on the bases in Iraq caused no casualties, raising hopes that the standoff over the killing of Gen. Qassem Soleimani would end relatively peacefully, though Iran has sent mixed signals over whether its retaliation is complete.

If the U.S. or Canada were to present incontrovertible evidence that the plane was shot down by Iran, even if unintentionally, it could have a dramatic impact on public opinion in Iran.

The Iranian public had rallied around the leadership after the killing of Soleimani last Friday, with hundreds of thousands joining the general's funeral processions in several cities, in an unprecedented display of grief and unity.

But sentiments in Iran are still raw over the government's crackdown on large-scale protests late last year sparked by an economic crisis exacerbated by U.S. sanctions. Several hundred protesters were reported to have been killed in the clampdown.

Those fissures could quickly break open again if Iranian authorities are seen to be responsible for the deaths of 176 people, mainly Iranians or dual Iranian-Canadian citizens. Iran still points to the accidental downing of an Iranian passenger jet by U.S. forces in 1988 — which killed all 290 people aboard — as proof of American hostility.

U.S., Canadian and British officials said Thursday it is "highly likely" that Iran shot down the Boeing 737, which crashed near Tehran early Wednesday. U.S. officials said the jetliner might have been mistakenly identified as a threat.

Canadian Prime Minister Justin Trudeau, whose country lost 57 citizens in the downing, said "we have intelligence from multiple sources including our allies and our own intelligence."

"The evidence indicates that the plane was shot down by an Iranian surface-to-air missile," he said.

The U.S. officials did not say what intelligence they had that pointed to an Iranian missile, believed to be fired by Russian Tor system, known to NATO as the SA-15. But they acknowledged the existence of satellites and other sensors in the region, as well as the likelihood of communication interceptions and other similar intelligence.

Western countries may hesitate to share information on such a strike because it comes from highly classified sources.

Videos verified by The Associated Press appear to show the final seconds of the the ill-fated airliner, which had just taken off from Iran early Wednesday.

In one video, a fast-moving light can be seen through the trees as someone films from the ground. The light appears to be the burning plane, which plummets to the earth as a huge fireball illuminates the landscape.

Someone off-camera says in Farsi: "The plane has caught fire. ... In the name of God, the compassionate, the merciful. God, please help us. Call the fire department!"

Ukraine's President Volodymyr Zelenskiy said "the missile theory is not ruled out, but it has not been confirmed yet."

In a Facebook post, he reiterated his call "on all international partners" — the U.S., Britain and Canada in particular — to share data and evidence relevant to the crash. He also announced plans to discuss the investigation with U.S. Secretary of State Mike Pompeo later on Friday.

Pompeo also called Canadian Foreign Minister François‑Philippe Champagne to offer his condolences for the Canadians who perished in the crash and offered "U.S. support for full cooperation with any investigation," the State Department said.

Ukraine's Foreign Minister Vadym Prystaiko tweeted that he and the president met with U.S. Embassy officials Friday and obtained "important data" about the crash. The minister didn't specify what kind of data it was, but said it would be "processed by our specialists."

In an interview with Fox News' Laura Ingraham that aired late Thursday, Pompeo said commercial airliners need to know if it is safe to fly into and out of Tehran.

"If the international community needs to shut down that airport, so be it," he said. "We need to get to the bottom of this very, very quickly."

Germany's Lufthansa airline said it and subsidiaries are canceling flights to and from Tehran for the next 10 days as a precautionary measure, citing the "unclear security situation for the airspace around Tehran airport." Other airlines have been making changes to avoid Iranian airspace.

Britain's Foreign Office has advised against all travel to Iran, and against all air travel to, from or within the country.

Iran's state-run IRNA news agency quoted Foreign Ministry spokesman Abbas Mousavi as saying Iran "has invited both Ukraine and the Boeing company to participate in the investigations." He later said a 10-member Canadian delegation was heading to Iran to assist victims' families.

Iran had initially said it would not allow Boeing to take part in the probe, going against prevailing international norms on crash investigations. It later invited the U.S. accident-investigating agency to take part in the investigation.

The National Transportation Safety Board said late Thursday that it would "evaluate its level of participation," but its role could be limited by U.S. sanctions on Iran. U.S. officials have also expressed concern about sending employees to Iran because of the heightened tensions.

U.S. Treasury Secretary Steven Mnuchin said Friday that his department would grant licenses to allow global investigators to travel to Iran and participate in the investigation.

Under rules set by a United Nations aviation organization, the NTSB is entitled to participate because the crash involved a Boeing 737-800 jet that was designed and built in the U.S.

The French air accident investigation agency, known by the French acronym BEA, is also taking part in the probe. The plane's engine was designed by CFM International, a joint company between French group Safran and U.S. group GE Aviation.

A preliminary Iranian investigative report released Thursday said that the airliner pilots never made a radio call for help and that the burning plane was trying to turn back for the airport when it went down.

The Iranian report suggested that a sudden emergency struck the Boeing 737, operated by Ukrainian International Airlines, just minutes after taking off from Imam Khomeini International Airport early Wednesday.

Those findings are not inconsistent with the effect of a surface-to-air missile. Such missiles are designed to explode near aircraft, shredding them with shrapnel. There is no need to score a direct hit, and a stricken plane may look like it is turning back when in fact it is disintegrating.

Abedzadeh, the senior aviation official, said authorities have recovered two black box flight recorders, saying they are "damaged" but readable. They may shed further light on what caused the crash.

Confronted by persistent questions about his military action in the Middle East, President Donald Trump and his top officials offered a string of fresh explanations Friday, with Trump now contending Iranian militants had planned major attacks on four U.S. embassies.

Just hours earlier, Secretary of State Mike Pompeo had said the U.S. didn't know when or where attacks might occur. Trump and other officials insisted anew that Iranian Gen. Qassem Soleimani had posed an imminent threat to the U.S., but they rebuffed repeated attempts to explain what they meant by "imminent."

Trump, meanwhile,  announced additional sanctions against Iran, which he had promised after a barrage of missiles fired by the Islamic State against American bases in Iraq earlier this week.

Those Iranian missiles, which caused no casualties, were prompted by the U.S. drone strike that killed Gen. Qassem Soleimani last week in Baghdad. That U.S. assault set off a chain of events that may have included the downing of a Ukrainian jetliner, possibly by an Iranian missile, and calls by the Iraqi government to expel U.S. troops from their country.

At the White House, Trump issued an executive order adding additional U.S. sanctions to the already long list his administration had imposed in an effort to force Iran to accept a new agreement that would curb its nuclear program and to halt support for militant groups throughout the Middle East.

Trump declared the U.S. was holding Iran responsible for attacks against the United States as well as a threat to U.S. service members, diplomats and civilians — an apparent reference to the justification for killing Soleimani.

"The United States will continue to counter the Iranian regime's destructive and destabilizing behavior," he said.

But Trump and others faced continuing questions over their claims of an "imminent" threat. Members of Congress said Pompeo and other officials did not provide sufficient detail or justification in briefings this week.

Define what you mean by imminent, Pompeo was asked Friday at a White House news conference.

Secretary of State Mike Pompeo and Treasury Secretary Steve Mnuchin brief reporters about additional sanctions placed on Iran, at the White House, Friday, Jan. 10, 2019, in Washington. AP Photo

"I don't know exactly which minute," Pompeo said. "We don't know exactly which day it would have been executed, but it was very clear. Qassem Soleimani himself was plotting a broad, large-scale attack against American interests and those attacks were imminent."

Both Pompeo and Trump had said U.S. embassies were threatened. The secretary of state broadened it to include "American facilities," including military bases throughout the region. "This was going to happen, and American lives were at risk," he said.

Trump gave a more worrisome number but still no specifics in a later comment.

"I can reveal that I believe it probably would've been four embassies," he told Fox News in an interview taped Friday.

He spoke amid revelations by U.S. officials that the American military had tried, but failed, to kill another senior Iranian commander on the same day that Soleimani was killed. The targeting of Abdul Reza Shahlai was apparently part of an effort to cripple the leadership of Iran's Quds Force, which the U.S. has designated a terror organization along with the larger Islamic Revolutionary Guard Force.

House Speaker Nancy Pelosi called the killing of Soleimani "provocative and disproportionate," and other members said they were unconvinced after a closed-door briefing on the intelligence.

"President Trump recklessly assassinated Qasem Soleimani," said Rep. Pramila Jayapal, a Washington state Democrat. "He had no evidence of an imminent threat or attack."

The new sanctions were in immediate response to Iran's firing of a barrage of missiles at American bases in neighboring Iraq this week after the killing of Soleimani. No one was injured. The larger U.S. goal is to force Iran to negotiate a new agreement on limiting its nuclear program.

In 2018, Trump withdrew from the nuclear agreement signed under President Barack Obama that traded curbs on the program for the easing of sanctions. Since then, the administration has added additional economic measures that have created hardship in Iran and brought its oil revenue to historic lows but have failed to bring the Iranian government to the negotiating table.

The sanctions added Friday include measures aimed at eight senior Iranian officials involved in what Treasury Secretary Steven Mnuchin called "destabilizing" activities throughout the Middle East as well as Tuesday's missile barrage.

Those measures, which would freeze any assets the officials have in U.S. jurisdiction and prohibit financial transactions with them, are largely symbolic since such senior figures are unlikely to have assets under American control after decades of hostility between the two nations.

But other measures announced Friday could have a significant effect on strategically important sectors of the Iranian economy, said Ben Davis, chief research officer at research and data analytics firm Kharon.

The executive order grants the administration power to place anyone involved, even indirectly, in the construction, manufacturing, textile or mining sector on a global financial blacklist. It also targets 17 of the largest steel and iron manufacturers — one of the few growth spots in the hobbled Iranian economy — along with three foreign companies, including two based in China, under secondary sanctions.

"It sends a signal to other foreign firms that continue to do business with Iranian steel producers that this is off limits," said Davis, a former Treasury Department official.

Adnan Mazarei, a senior fellow at the Peterson Institute for International Economics, said the sanctions will hurt an Iranian economy that was forced to cut fuel subsidies earlier this year, triggering nationwide protests, but they also will make it harder for government to negotiate with the U.S.

"This will be seen as another sign that the U.S. government cannot be taken at its word when it says it wants to negotiate," Mazarei said.

Mnuchin insisted the sanctions are working and have deprived Iran of tens of billions of dollars. "They would be using that for terrorist activities throughout the region and to enable them to do more bad things," he said. "And there's no question, by cutting off the economics to the region, we are having an impact."

Unknown gunmen shot dead a reporter and a cameraman on Friday after they covered anti-government protest in Iraq's southern city of Basra, the Dijlah TV channel said.

The reporter, Ahmed Abdul Samad, and the cameraman, Safaa Ghali, worked for the Dijlah TV. They were shot dead inside their car while they were leaving the protest site in Basra, south of the Iraqi capital Baghdad, the report said.

The killing came as massive demonstrations were held during the day in Baghdad and nine of Iraqi central and southern provinces, renewing their demands for comprehensive reforms, including nominating an independent prime minister to form a new government to prepare for early general elections.

The demonstrators also condemned the United States and Iran for what they described as interference in the internal affairs of Iraq and turning Iraq to an arena to settle their accounts.

In the past week, the U.S. killed a senior Iranian commander in a drone attack near the Baghdad International Airport, and Iran fired on Wednesday more than a dozen of missiles at two Iraqi bases housing U.S. troops in retaliation.

Mass anti-government demonstrations have continued in Iraq since last October, demanding comprehensive reform, fight against corruption, better public services and more jobs.

The Islamic State group gloated over the recent U.S. killing of a senior Iranian general, who rose to prominence by advising forces fighting the extremists.

In the first IS comments since Gen. Qassem Soleimani's slaying, the group said his death "pleased the hearts of believers." The editorial was released in the group's al-Nabaa online newspaper late Thursday.

Although the U.S. and Iran strictly avoided working together directly, they were once on the same side in the fight against IS. Neither side wants to see the extremists stage a comeback.

But as the various players in Iraq jockey to come out ahead in a post-Soleimani landscape, Islamic State militants may find an opening. Thousands of fighters are scattered among the group's sleeper cells, and have claimed attacks in both Iraq and neighboring Syria in recent months.

As the head of Iran's elite Quds Force, Soleimani was one of the main commanders on the ground spearheading the fight against IS. He sent thousands of Iran-backed fighters to Iraq and Syria to battle the extremists, and directed Iraqi Shiite militias as well. A top Iraqi militia commander was killed alongside Soleimani in last week's U.S. drone strike.

The IS editorial said that its members tried for years to kill the two commanders, but that "God brought their end at the hands of their allies." It said both men "have gone too far in shedding the blood of Muslims in Iraq and Syria."

Iraq's caretaker prime minister has now asked Washington to start working out a road map for withdrawing the more than 5,000 American troops in Iraq, in response to Soleimani's killing. But the U.S. State Department on Friday bluntly rejected the request.

Iraqis have felt furious and helpless at being caught in the middle of fighting between Baghdad's two closest allies.

Iraq's caretaker prime minister asked Washington to work out a road map for an American troop withdrawal, but the U.S. State Department on Friday bluntly rejected the request, saying the two sides should instead talk about how to "recommit" to their partnership.

Thousands of anti-government protesters turned out in the capital and southern Iraq, many calling on both Iran and America to leave Iraq, reflecting their anger and frustration over the two rivals — both allies of Baghdad — trading blows on Iraqi soil.

The request from Prime Minister Adel Abdul-Mahdi pointed to his determination to push ahead with demands for U.S. troops to leave Iraq, stoked by the American drone strike on Jan. 3 that killed top Iranian Gen. Qassem Soleimani. In a phone call Thursday night, he told U.S. Secretary of State Mike Pompeo that recent U.S. actions were unacceptable breaches of Iraqi sovereignty and a violation of their security agreements, his office said.

He asked Pompeo to "send delegates to Iraq to prepare a mechanism" to carry out the Iraqi Parliament's resolution on withdrawing foreign troops, according to the statement.

"The prime minister said American forces had entered Iraq and drones are flying in its airspace without permission from Iraqi authorities, and this was a violation of the bilateral agreements," the statement added.

Abdul-Mahdi signaled he was standing by the push for U.S. forces to leave despite signs of de-escalation by Tehran and Washington after Iran retaliated for Soleimani's death by firing missiles that hit two Iraqi bases where American troops are based but caused no casualties.

Iraqis feel furious and helpless at being caught in the middle of the fighting. Abdul-Mahdi has said he rejects all violations of Iraqi sovereignty, including both the Iranian and U.S. strikes.

The State Department flatly dismissed Abdul-Mahdi's request, saying U.S. troops are crucial for the fight against the Islamic State group and it would not discuss removing them.

Pompeo indicated Friday the troops would remain, adding that the U.S. would continue its mission to help train Iraqi security forces and counter the Islamic State group.

"We are happy to continue the conversation with the Iraqis about what the right structure is," Pompeo said at the White House during an unrelated appearance.

 "Our mission set there is very clear. We've been there to perform a training mission to help the Iraqi security forces be successful and to continue the campaign against ISIS, to continue the counter-Daesh campaign," he said, using alternate acronyms for the militant group.

"We're going to continue that mission but, as times change and we get to a place where we can deliver upon what I believe and what the president believes is our right structure with fewer resources dedicated to that mission, we will do so," Pompeo said.

He said a NATO team was at the State Department working on a plan "to get burden- sharing right in the region, as well, so that we can continue the important missions to protect and defend, and keep the American people safe" while reducing costs and burdens borne by the U.S.

Earlier in the day, Pompeo's spokeswoman Morgan Ortagus said any delegation sent to Iraq would be dedicated to "discussing how to best recommit to our strategic partnership - not to discuss troop withdrawal, but our right, appropriate force posture in the Middle East."

Iraqi lawmakers passed a resolution Sunday to oust U.S. troops, following the U.S. drone strike that killed Soleimani and senior Iraqi militia commander Abu Mahdi al-Muhandis at Baghdad's airport. The nonbinding vote put the responsibility on the government to formally request a withdrawal. Abdul-Mahdi urged lawmakers at the time to take "urgent measures" to ensure the removal of the troops.

In speaking to Pompeo, Abdul-Mahdi stopped short of requesting an immediate withdrawal, allowing time to draw up a strategy and timeline for departure.

In its initial readout of the call, the State Department made no mention of Abdul-Mahdi's request on the troops. It said Pompeo, who initiated the call, reiterated the U.S. condemnation of the Iranian missile strikes and underscored that President Donald Trump "has said the United States will do whatever it takes to protect the American and Iraqi people and defend our collective interests."

There are some 5,200 U.S. troops in Iraq assisting and providing training to Iraqi security counterparts to fight IS. An American pullout could deeply set back efforts to crush remnants of the group amid concerns of its resurgence during the political turmoil.

Both the U.S. and Iran have fought to defeat IS, and neither wants to see it stage a comeback.

IS gloated in its first comments on Soleimani's slaying, saying his death "pleased the hearts of believers," in an editorial in the group's al-Nabaa online newspaper. It carried a photo of Soleimani and al-Muhandis, saying that "God brought their end at the hands of their allies."

U.S. Assistant Secretary of State David Schenker said future talks between Baghdad and Washington were expected to focus on the nature of their strategic relationship,

"We provide assets that no other coalition ally can provide. ... If the United States wasn't in Iraq, it's hard to imagine the coalition being in Iraq," he told reporters in Dubai at the end of a visit to the region in which he met with Iraqi officials in the northern Kurdish region.

Schenker added that the U.S. and its partners have provided $5.4 billion to the Iraqi military in the last four years.

Ortagus said the U.S. and Iraqi governments need to talk about security as well as "our financial, economic and diplomatic partnership." She did not elaborate.

Iraq is highly dependent on Iran sanctions waivers from Washington to continue importing Iranian gas to meet electricity demands, and the U.S. has consistently used this as leverage. The current waiver expires in February, and without a new one, Iraq could face severe financial penalties.

The demand for a troop withdrawal is not universal among Iraqis. Sunni and Kurdish lawmakers, who oppose the Parliament resolution, see the U.S. presence as a bulwark against domination by the majority Shiites and Iran. Kurdish security forces have benefited from U.S. training and aid.

Protesters criticized the ongoing crisis involving Iraq, the U.S. and Iran in demonstrations across the capital and in the southern provinces.

Thousands massed in Baghdad's Tahrir square, the epicenter of the protest movement, and many chanted "Damn Iran and America!" Large demonstrations also were held in Basra, Dhi Qar, Najaf and Diwanieh provinces as the movement seeks to regain momentum after regional tensions overshadowed the uprising.

Amid the protests in Basra, Iraqi journalist Ahmed Abdul Samad was found dead in his car outside a police station from a gunshot wound to the head, according to a security official who requested anonymity in line with regulations. A photographer covering the protests was injured and is in critical condition.

Meanwhile, Grand Ayatollah Ali al-Sistani urged rival political factions to unite and put private interests aside, saying they risked creating more unrest. The factions have yet to agree on a nominee to replace the outgoing Abdul-Mahdi, who resigned in December under pressure from the protesters.

"Everyone is required to think carefully about what this situation will lead to if there is no end to it," he added.