By Agence France-Presse Prime Minister Justin Trudeau said Thursday multiple intelligence sources indicate that Iran shot down a Ukrainian airliner after it took off from Tehran, killing all 176 onboard, including 63 Canadians. Mourners in Toronto console each other during a vigil for the victims of Ukrainian Airlines flight 752 which went down in Iran, killing everybody aboard (AFP / Geoff Robins / MANILA BULLETIN) Trudeau's comments came as video emerged that appeared to show the moment the airliner was hit. That and other footage posted on social media increasingly pointed to a catastrophic mistake by Tehran's air defense batteries in bringing down Ukraine International Airlines Flight PS752 early Wednesday. The video, which The New York Times said it verified, shows a fast-moving object rising at an angle into the sky before a bright flash is seen, which dims and then continues moving forward. Several seconds later an explosion is heard. Citing information from allies as well as Canada's own intelligence, Trudeau said the plane appeared to have been hit by an Iranian surface-to-air (SAM) missile. "We know this may have been unintentional. Canadians have questions, and they deserve answers," Trudeau told reporters. He was backed by other Western leaders, including British Prime Minister Boris Johnson who said mounting evidence supported a missile strike, which "may well have been unintentional." US President Donald Trump indicated that Washington officials believed the Kiev-bound Boeing 737 was struck by one or more Iranian missiles before it ditched and exploded outside Tehran. The US National Transportation Safety Board late Thursday said it had received formal notification of the crash from Iran and would send a representative to join the crash probe. Iran's foreign ministry earlier invited the US planemaker Boeing to "participate" in the inquiry. The flight went down in the dark just minutes after takeoff, with no radio message from the pilot to indicate distress, according to the Iranian Civil Aviation Organization. It was carrying 82 Iranians, 63 Canadians, 11 Ukrainians, 10 Swedes, four Afghans, three Germans and three Britons. With tensions high between the United States and Iran, the disaster unfolded just hours after Tehran launched ballistic missiles towards bases in Iraq housing US troops. Iran retaliated for the January 3 US drone strike in Baghdad that killed a top Iranian general. The Iranian government said the missile strike scenario made "no sense," however, arguing that several internal and international flights had been sharing approximately the same airspace. Tehran later asked Ottawa to share its information with Iranian investigators. 'Canadians want answers'  Trudeau said Canada was working with allies to ensure a credible probe. "The families of the victims want answers, Canadians want answers, I want answers," he said. AFP / Dave Chan Canadian Prime Minister Justin Trudeau's comments came as video, and images posted on social media, increasingly pointed to a catastrophic mistake by Tehran's air defense batteries "This government will not rest until we get that." Canada's transportation safety board on Thursday said it had accepted an invitation from Iran's civil aviation authority to join the inquiry. Britain's Johnson called Thursday for a full, transparent investigation. 'I have my suspicions'  Trump would not directly confirm what US intelligence was saying privately. "I have my suspicions," Trump said, adding that "somebody could have made a mistake." But unnamed officials told US media that satellite, radar and electronic data indicated Tehran's air defense units downed the aircraft. ABC News reported that an unnamed official said it was "highly likely" the plane was brought down by two SAMs.