Trudeau said Wednesday 138 passengers on the flight were connecting to Canada. The flight included many international students who were studying at universities across Canada. Newlyweds and a Canadian family of four were also on the flight.

Trudeau said his government is pushing to be part of the Iranian-led investigation of the plane crash near Tehran that killed everyone on board. Getting answers from Iran might prove difficult as Canada closed its embassy in Iran in 2012 and suspended diplomatic relations.

The crash of the Ukraine International Airlines plane came hours after Iran launched a ballistic missile attack on Iraqi bases housing U.S. soldiers, but Iranian officials said they suspected a mechanical issue brought down the 3½-year-old Boeing 737-800 aircraft. Ukrainian officials initially agreed, but later backed away and declined to offer a cause while the investigation is ongoing.

"There is a clear need for answers," Trudeau said. "Canada is very concerned on this."

Trudeau said he spoke with President Donald Trump earlier Wednesday. U.S. Secretary of State Mike Pompeo said the United States is calling for cooperation with any investigation into the cause of the crash

Asked if he could say whether the plane was shot down or not, Trudeau said: "I cannot. It's too early to speculate."

Trudeau said Canadian victims' families want and deserve answers.

"Know that all Canadians are grieving with you," Trudeau said.

Transport Minister Marc Garneau said he could not speculate but said that soon after the departure of the plane contact was lost. He said the black box information is needed.

Authorities said they found the plane's so-called black boxes, which record cockpit conversations and instrument data. But it was not immediately clear how much access to the information the Iranians would allow.

Canada is offering technical assistance to the upcoming investigation in Iran. Canada's Transportation Safety Board said it has appointed an expert to monitor the progress which is being led by Iran's civil aviation organization.

Aviation experts were skeptical about Iran's initial claim that the plane was brought down by a mechanical problem.

"Something unusual happened," Garneau said.

The plane carried 167 passengers and nine crew members from different nations. The Canadian flag on Parliament Hill was lowered to half-mast. The U.S. embassy in Ottawa also lowered its flag.

Canadian Foreign Minister François-Philippe Champagne confirmed at least 63 Canadians died and as more information becomes available, including details on dual citizens, the number of deceased Canadians could change.

It's one of the worst losses of life for Canadians in an aviation disaster. In 1985 a bomb exploded and killed 329 people aboard an Air India flight. Air India Flight 182 from Montreal to New Delhi exploded over the Atlantic Ocean near Great Britain on June 23, 1985. Most of the victims were Canadian.

The Tehran to Toronto route via Kyiv is an affordable route for Iranian Canadians and international students. There are no direct flights.

Younes Zangiabadi, a board member of the Iranian Canadian Congress, said because of U.S. sanctions, there are many options for Iranian-Canadians to travel to Iran.

Payman Paseyan, a member of the Iranian-Canadian community in Edmonton, Alberta, said about 27 people from Edmonton, a family of four that he knew, were on the flight. Two professors from the University of Alberta, Pedram Mousavibafrooei and Mojgan Daneshmand, and their daughters Daria and Dorina died. He said he often would go to the gym with the father and described him as a nice guy who often visited his former restaurant with his family. "It's just terrible," he said.

He said most of victims were visiting family in Iran over the holidays and that many were dual citizens and many were international students. "One of the reasons why you take that flight is you wouldn't want to take a flight that has a connection in the United States because international students can't do that," he said.

Paseyan said members of the Iranian-Canadian community learned of the crash while being glued to the news after Tuesday's missile attacks in Iraq.

He said there are questions about what caused the crash but said that's not the focus right now.

"Whether it's a missile, mishap or a technical issue or whatever, we want our community members. We lost one percent of our Edmonton Iranian community members on that flight. It's just terrible," he said.

Many international students were confirmed among the crash victims — four from Western University, three from the University of Ottawa, and two from the University of Guelph. The University of Toronto said the names of six of their students were on the flight manifest.

The University of Guelph in Canada said Ghanimat Azhdari was a student in the department of geography and Milad Ghasemi was a student in marketing.

Western University said three current graduate students died and one was an incoming graduate student. They did not name the students. The University of Waterloo also said two PhD students' names were on a list of passengers provided by the airline.

In a letter to parents, the principal of Northern Secondary School says the school is grieving the loss of Maya Zibaie, a Grade 10 student.

A dentistry in Aurora, Ontario confirmed that Parisa Eghbalian, a dentist, and her daughter Reera Esmaeilion died. Eghbalian's husband, Hamed Esmaeilion, is also a dentist at E&E Dentistry, but was not travelling with his wife and child.

Canada is urging Canadians to avoid non-essential travel to Iran due to the volatile security situation, but the travel advisory makes no mention of the plane crash.

"There are no words. 176 lives lost. 63 Canadians won't be coming home," opposition New Democrat leader Jagmeet Singh tweeted.