The Ukrainian airliner that crashed killing 176 people was likely downed in error by an Iranian missile, Canadian Prime Minister Justin Trudeau said Thursday.

At a news conference, Trudeau confirmed intelligence from various sources led to that conclusion, but only a “full and credible investigation” could definitely confirm it.

“We have intelligence from multiple sources, including our allies and our own intelligence, Trudeau said. “The evidence indicates that the plan was shot down by an Iranian surface-to-air missile. This may well have been unintentional.”

He indicated that conclusion will hit families hard coming soon after the news of the crashed plane.

“The news will undoubtably come as a further shock to the families who are already grieving the face of this unspeakable tragedy.” Trudeau said.

But the prime minister said the government would not rest until the cause of the downing of the plane was known.

“The families of the victims and all Canadians want answers,” Trudeau said. “I want answers. That means closure, transparency, accountability and justice. This government will not rest until we get that.”

The Boeing 737-800 was just airborne from an Iranian airport Wednesday when it crashed. There were 63 Canadians on board, and 138 passengers flying to Canada. Most passengers were Iranian or Iranian Canadians bound for the Ukrainian capital of kyiv.

Trudeau refused to blame U.S. President Donald Trump, whose action in killing by drone the Iranian military commanders, Qassem Soleimani, resulted in Iran firing missiles into Iraq in retaliation.

“The evidence suggests that this is the likely cause but we need to have a full and complete and credible investigation to establish exactly what happened,” Trudeau said. “That’s what we are calling for and that’s what we’re expecting will happen.”

A few hours after the Iraq attack, which Trudeau condemned, the airline crashed.

While a 45-man team from the Ukraine has arrived to take part in the crash investigation, Trudeau said Canada’s participation has not yet been confirmed, despite a firm request from Canada.