Iranian officials have ruled out a missile strike, and initially said the plane appeared to have crashed because of technical difficulties.
A preliminary Iranian investigative report released on Thursday said the pilots never made a radio call for help and that the aircraft was trying to turn back for the airport when the burning plane went down.
Trudeau’s accusation came as new amateur footage appeared to show a missile hurtling towards the plane before a bright flash lit up the sky and large boom rocked Parand, near Tehran’s airport.
Analysis by the Bellingcat investigative website, which did groundbreaking work in the wake of the downing of Malaysia Airlines flight MH17 over Ukraine in 2014, suggests the video is genuine.
Other unverified images from the charred crash site appear to show shrapnel damage to sections of the plane’s fuselage.
The Ukraine International Airlines crash killed 176 passengers and crew on Wednesday — just as the region was gripped by a heightened state of alert over Iran’s decision to launch ballistic missiles on military bases in Iraq housing US troops.
In addition to the Canadians, there were 82 Iranians, 11 Ukrainians and 10 Swedish nationals on board the doomed flight, as well as four Afghans, three Germans and three Britons.
“What happened yesterday was a tragedy. A tragedy that shocked not only Canada but the entire world,” Mr Trudeau said.
“We have intelligence from multiple sources, including our allies and our own intelligence, that the plane was shot down by an Iranian surface-to-air missile. This may well have been unintentional.
“The families of the victims and all Canadians want answers. I want answers. That means closure, transparency, accountability and justice.”
Mr Trudeau did not rule out the possibility the aircraft was intentionally targeted but said evidence suggested the missile launch was probably a mistake.
Prime Minister Scott Morrison was more definitive, telling 2GB on Friday morning: “This is not a deliberate attack — it’s a terrible accident.” He said Australia had similar intelligence to other allies that an Iranian missile downed the plane.
Mistaking a commercial passenger jet for an American war plane would be deeply embarrassing for the Iranian leadership and its military, which has not responded to Canada’s allegations.
American officials told multiple media outlets that they had radar images showing the “blip” of a missile launch, followed by another “blip” indicating the weapon had struck the flight about 8000 feet, just minutes after the plane took off from Tehran.
US President Donald Trump said he had a feeling something “very terrible” had happened and “somebody could have made a mistake”.
Asked what he thought brought down the plane, Trump replied: “Well, I have my suspicions”.
“It was flying in a pretty rough neighbourhood. Some people say it was mechanical, I personally don’t even think that is a question,” he said.
Iran has strenuously denied it shot down the plane and has repeatedly blamed its downing on a mechanical fault such as a catastrophic engine explosion.
It was not revealed whether US officials believed Iran deliberately or accidentally shot down the plane, however the incident and Tehran’s subsequent denials will trigger a new round of tensions in the already volatile Middle East.
Mr Trudeau said Iran wanted to keep the flight’s crucial black boxes in Iran but will apparently allow Ukrainian investigators access to the data. There are reports the regime has started tampering with the crash site.
The Canadian leader was repeatedly asked whether America was partly responsible for the loss of the flight given its assassination of top Iranian general Qassem Soleimani had escalated tensions in the Middle East.
“I think that is one of the many questions that people will be thinking about and trying to find answers to,” Trudeau said.
The disaster has the hallmarks of Malaysia Airlines flight MH17, which was shot down over Ukraine by a Russian-made Buk surface-to-air missile in 2014, killing all 298 passengers and crew members, including 38 Australian citizens and residents.
Ukraine initially agreed with Iran’s assessment that mechanical or technical error was to blame for this week’s crash but quickly walked back from that amid mounting evidence of foul play.
The secretary of Ukraine’s national security council, Oleksiy Danylov, told Ukrainian media that investigators wanted to search for the possible debris of a Russian-made missile at the crash site near Tehran’s main airport, citing images that suggested the aircraft fuselage suffered shrapnel damage.
British Prime Minister Boris Johnson also said there was a “body of evidence” the plane had been destroyed by a missile.
A preliminary report by Iran’s civil aviation authority said the pilots never made a radio call for help. The report also claimed the plane was attempting to turn back to the airport when it caught fire and exploded on impact.
Ukraine International Airlines said the doomed plane was built in 2016 and had been serviced just two days before it crashed.
Bevan Shields is the Europe correspondent for The Sydney Morning Herald and The Age.