Iranian security forces used heavy gunfire against protesters in a Kurdish town in the country's west on Monday, killing at least five during an anti-government protest that erupted at the funeral of two people killed the day before, activists said.

Videos circulating online show dozens of protesters taking shelter in alleyways as heavy gunfire echoes through the streets. Some show individuals lying motionless and bloodied in the streets, while others show residents gathering at a local hospital to donate blood.

Iran has been convulsed by anti-government protests since the Sept. 16 death of 22-year-old Mahsa Amini, a Kurdish woman who died in the custody of the country's morality police in the capital, Tehran. The protests, which were initially concentrated in the western, Kurdish region of Iran where Amini was from, have spread across the country and escalated into calls for the overthrow of Iran's ruling clerics.

Hengaw, a Kurdish human rights group, said Iranian security forces unleashed heavy gunfire on protesters in the town of Javanrud, where a funeral was held for two protesters killed the day before. It cited witnesses as saying that Iranian forces used heavy machine guns.

Read more: Iran sentences anti-government protester to death: Report

Hengaw said seven people were killed on Monday, while another group, the Kurdistan Human Rights Network, put the toll at five. The latter group said many of the wounded were being treated in homes because of fears they could be arrested from hospitals, making it difficult to confirm the toll. It said several were shot in the head or chest.

Iranian authorities heavily restrict media coverage of the protests and have periodically shut off internet access, making it difficult to confirm details of the unrest.

The semiofficial Fars news agency reported protests in Javanrud on Sunday night, saying security forces were fired upon with live ammunition. It said two people were killed and four wounded.

Later on Monday, state TV interviewed a local security official, Mohammad Pourhashemi, who blamed the shooting in Javanrud on local gunmen who he said had exchanged fire with security forces. The report did not provide further details.

Read more: Iran’s elite technical university emerges as hub of protests

Funerals have often been the scene of renewed protests in recent weeks, as they were during the 1979 Islamic Revolution that brought the clerics to power. The latest demonstrations mark the biggest challenge to the theocracy in over a decade.

At least 426 people have been killed and more than 17,400 arrested, according to Human Rights Activists in Iran, a group monitoring the unrest. It says at least 55 members of the security forces have been killed.

Jalal Mahmoudzadeh, a lawmaker representing the Kurdish city of Mahabad, told the Etemad daily that 11 people have been killed during protests in the city since late October, many of them in recent days. He said some members of the security forces fired upon homes and businesses on Saturday, and he called on authorities to adopt a softer touch.

The unrest cast a shadow over the World Cup on Monday, where the Iranian national team faced off against England. Iran's players did not sing along to their national anthem, and some fans chanted Amini's name at the 22nd minute of the match.

The violence has also spilled across the border into neighboring Iraq's northern Kurdish region. Iran has blamed the unrest at home in part on Kurdish groups based in Iraq, and has targeted them with missile and drone attacks.

Iran said Monday that its latest strikes were necessary to protect the country's borders, while Kurdish officials condemned the attacks as unprovoked aggression. Iraq's central government, which is dominated by parties close to Iran, also condemned the strikes.

A strike late Sunday killed a member of the Democratic Party of Iranian Kurdistan, said Mohammed Nazif Qaderi, a senior official in the Kurdish Iranian group living in exile in Iraq.

The group said Iranian surface-to-surface missiles and drones hit its bases and adjacent refugee camps in Koya and Jejnikan. The group also asserted that the strikes had hit a hospital in Koya.

The Iranian strikes come in the wake of a visit to Baghdad last week by Esmail Ghaani, the commander of Iran's elite Quds Force. During the visit, Ghaani threatened Iraq with a ground military operation in the country’s north if the Iraqi army does not fortify the border.

Some Kurdish groups have been engaged in a low-intensity conflict with Tehran since the 1979 revolution. Iran accuses them of inciting protests in Iran and smuggling weapons into the country, allegations the Kurdish groups have denied. Iran has not provided evidence to back up the claims.

On Monday, Iranian Foreign Ministry spokesman Nasser Kanaani told reporters that Iran had acted to “protect its borders and security of its citizens based on its legal rights.” He alleged that the government in Baghdad and the Irbil-based administration of Iraq's autonomous Kurdish region had failed to implement purported commitments to prevent threats against Iran from Iraqi areas.

The government of the autonomous Kurdish region of Iraq condemned the strikes as a “gross infringement of international law and neighborly relations.”

Qaderi told The Associated Press the Kurdish opposition groups in Iraq support the protests in Iran, which he described as a reaction to “the policies of this regime” he said oppresses its people. He denied that his group has sent fighters or weapons to Iran.

He said that his group had moved fighters away from the border to avoid giving Iran an “excuse” for further attacks. He called on the international community to prevent further aggression by Iran.

The United States condemned the latest Iranian strikes. “Such indiscriminate and illegal attacks place civilians at risk, violate Iraqi sovereignty, and jeopardize the hard-fought security and stability of Iraq and the Middle East," Gen. Michael E. Kurilla, who heads U.S. Central Command, said in a statement.

Sunday's Iranian strikes in northern Iraq come a day after Turkey launched deadly airstrikes over northern regions of Syria and Iraq, targeting Kurdish groups that Ankara holds responsible for last week’s bomb attack in Istanbul.

On Monday, Turkish officials said suspected Kurdish militants in Syria fired rockets into the border town of Karkamis in Turkey, killing two people, including a teacher and a 5-year-old boy.