All 176 people on the Boeing 737-800, including at least 63 Canadians, were killed. Trudeau said at a press conference that he was calling for a "thorough and credible investigation" into the crash.

Canada does not have diplomatic relations with Iran, but Trudeau said Iran had expressed "openness to Canadian involvement" when it comes to the investigation, though it wasn't clear to what degree.

He said that "Canadian expertise when it comes to air tragedies" is "world-class," adding, "We have lots to contribute, and we have lost much."

But he added that Iran had refused to let the black boxes from the crashed plane outside Iran. Trudeau said he understood that the Ukrainian government would be given access to the black boxes.

Reporters grilled Trudeau on whether he blamed the United States and President Donald Trump for escalating tensions with Iran by authorizing the strike that killed Iranian Maj. Gen. Qassem Soleimani last week.

American news outlets reported on Thursday that US officials believe that an Iranian surface-to-air missile system likely downed the plane by accident, since Iran's anti-aircraft systems were likely activated at the time of the crash.

But Trudeau avoided blaming Trump or the US, repeating his demand for a full investigation.

"I think it is too soon to be drawing conclusions or assigning blame or responsibility in whatever proportions," Trudeau said. "Recognizing that there is going to need to be a full and credible investigation into what happened before we draw conclusions."

The reporters also asked Trudeau about Trump saying earlier on Thursday that he did not believe the flight was downed as a result of a mechanical error.

"It was flying in a pretty rough neighborhood," Trump said. "Someone could have made a mistake."

Trudeau responded: "I'll let Mr. Trump's words stand for themselves."