Evidence suggests an Iranian missile brought down a Ukrainian passenger plane that crashed near Tehran, possibly in error, Canadian PM Justin Trudeau has said.
Mr Trudeau called for a full and thorough investigation into the crash, which killed all 176 people on board.
Iran has ruled out a missile strike by its air defences.
The crash came just hours after Iran carried out missile strikes on two airbases housing US forces in Iraq.
CBS News quoted US intelligence sources as saying a satellite detected infrared "blips" of two missile launches, followed by another blip of an explosion.
Meanwhile, Newsweek quoted a Pentagon and senior US intelligence officials, as well as an Iraqi intelligence official, as saying they believed Ukraine International Airlines flight PS752 was hit by a Russian-made Tor missile.
What does US media report? In separate reports, CBS News and Newsweek said US and Iraqi intelligence officials were confident the Ukrainian plane was brought down by a missile fired by Iran.
CBS published a brief report on Twitter. It said this information was based on US intelligence, which sources said picked up signals of a radar being turned on.
US satellites also reportedly detected two missile launches shortly before the Ukrainian plane exploded.
Meanwhile, Newsweek quoted US and Iraqi officials as saying they believed the aircraft was hit by a Russia-built Tor M-1 surface-to-air missile system.
Two Pentagon officials assessed that the incident was accidental, Newsweek added.
It quoted sources as saying that Iran's anti-aircraft systems were probably active following its attacks on the US airbases.
The Pentagon has so far made no public comment on the issue.
Chilling new video appears to show the moment an Iranian missile hit a Ukrainian passenger plane just moments before it crashed, killing all 176 people on board.
The footage emerged Thursday afternoon, hours after President Donald Trump revealed he has serious doubts the crash was caused by mechanical failure, as Iranian officials have claimed.
'It was flying in a pretty rough neighborhood. Somebody could have made a mistake,' Trump told reporters at the White House on Thursday. 'I have a feeling that something very terrible happened, very devastating.'
Canadian Prime Minister Justin Trudeau later echoed Trump's concerns, saying that evidence indicates an Iranian missile downed the and that the strike 'may have been unintentional'.
Trudeau said Canadian and allied intelligence supports that conclusion. He declined to get into the specific intelligence, but said it appeared it was a surface-to-air missile that struck the plane.
'The intelligence evidence suggests very clearly a possible and probable cause for the crash,' Trudeau told a news conference.
US intelligence officials are 'confident' that Iran shot down the Ukraine International Airlines Flight 752 after detecting a radar system being turned on before two missiles were launched, shortly before an explosion believed to have come from the jet, CBS reported.
Two Pentagon officials added that the missiles were likely launched in error by Iranian anti-aircraft crews awaiting a US response to Iran's rocket strikes against American bases in Iraq hours earlier, according to Newsweek.
Thursday morning, there was another piece in the puzzle to contend with: an unverified photograph from the crash site purporting to show the “seeker head” from a Russian-built Tor-M1 surface-to-air missile of the kind used by Iranian air defence units.
Hours later those suspicions appeared to become more concrete as US defence and intelligence officials supplied the alleged missing link that many had been waiting for.
They disclosed that the US had picked up the signature of an anti-aircraft missile battery locking on to the Ukrainian plane, and then the infrared heat signal of two missile launches followed by that of an explosion on the plane.
An NBC News animation illustrates what may have been the final moments of Flight PS752 in the skies above Tehran.
A Canadian scientist discovered the treatment for a disease that kills between 20 and 50 thousand people each year. She was killed in the crash of flight #PS752. #ukraineplanecrash Tehran
Iran has admitted "unintentionally" shooting down a Ukrainian passenger jet, killing all 176 people on board.
An investigation found that "missiles fired due to human error", President Hassan Rouhani said. He described the crash as an "unforgivable mistake".
The military said the jet turned towards a sensitive site belonging to Iran's Revolutionary Guards and was then mistaken for a cruise missile.
Iran had previously rejected suggestions that it was to blame.
The downing of Ukraine International Airlines flight PS752 on Wednesday came just hours after Iran carried out missile strikes on two airbases housing US forces in Iraq.
The strikes were a response to the killing of senior Iranian commander Qasem Soleimani in a US drone strike in Baghdad on 3 January.
