The destruction of the airliner, which carried 63 Canadians, “may well have been unintentional,” Trudeau told a news conference in Ottawa.

“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 Ukraine International Airlines flight to Kiev from Tehran crashed on Wednesday hours after Iran fired ballistic missiles at two U.S. military bases in Iraq, and Iranians were on high alert for a U.S. military response. tmsnrt.rs/36Fn26m

Trudeau said his government would not rest until it had obtained closure, transparency, accountability and justice.

Earlier on Thursday, a U.S. official, citing an extensive review of satellite data, said Washington had concluded with a high degree of certainty that anti-aircraft missiles brought down the plane. The official said the Boeing 737-800 (BA.N) had been tracked by Iranian radar.

The U.S. government believes Iran shot down the plane by mistake, three U.S. officials told Reuters.

The data showed the plane was airborne for two minutes after departing Tehran when the heat signatures of two surface-to-air missiles were detected, one of the officials said.

That was quickly followed by an explosion in the vicinity of the plane, this official said. Heat signature data then showed it on fire as it went down. Heat signatures are infrared emissions detected by U.S. military satellites.

Iran denied that the airliner had been hit by a missile, government spokesman Ali Rabiei said in a statement.