A video has emerged online which reportedly shows a missile being fired into Tehran's sky, before striking an object.
A bright flash can be seen around the same time that a Ukrainian plane crashed shortly after taking off from an airport in the Iranian capital.
News of the video came just hours after international intelligence suggested the airliner was shot down by an Iranian surface-to-air missile.
Canadian leader Justin Trudeau says evidence indicates the strike "may have been unintentional."
Prime Minister Scott Morrison says Australia has the same advice as Canada, echoing the position of Mr Trudeau.
"We have had similar intelligence as our partners have," Mr Morrison told 2GB radio on Friday.
"This is not a deliberate attack ... it's a terrible accident."
Prime Minister Justin Trudeau held a news conference in Ottawa, detailing intelligence suggesting the plane was downed by a missile. Source: The Canadian Press
"This may well have been unintentional," President Trudeau said in a press conference.
A total of 176 people, including 63 Canadians and 11 Ukrainians, were killed when the plane came down shortly after take-off on Wednesday, shortly after Iran launched missiles towards bases in Iraq housing US troops.
US 'suspicions'
United States President Donald Trump said Thursday he had "suspicions" about the crash as US media reported it had been mistakenly shot down by Iran.
Unnamed officials told US media that Iranian air defense systems likely accidentally shot down the airliner Wednesday.
Newsweek, CBS and CNN said that satellite, radar and electronic data indicated the tragic error, which followed a ballistic missile barrage by Iran on two military bases in Iraq where US troops work.
Mr Trump didn't directly confirm that conclusion, but strongly hinted at it.
"I have my suspicions," Mr Trump said. "It was flying in a pretty rough neighborhood and somebody could have made a mistake."
"Some people say it was mechanical. I personally don't think that's even a question," Mr Trump said, adding that "something very terrible happened."
Analysts pointed to pictures shared widely online of the wrecked fuselage of the aircraft showing multiple apparent puncture holes consistent with a rocket that detonated just outside the plane, blasting shrapnel into it.
'Rumours make no sense'
Iran ruled out a missile strike as the cause of the plane crash, saying such a scenario made "no sense."
"Several internal and international flights were flying at the same time in Iranian airspace at the same altitude of 2,440 metres," Iran's transport ministry said.
"This story of a missile striking a plane cannot be correct at all," it said in a statement.
"Such rumours make no sense," Ali Abedzadeh, head of Iran's civil aviation organisation and deputy transport minister, said in the statement.
Mr Abedzadeh said Iran and Ukraine were in the process of "downloading information" from black boxes retrieved from the crash site.
"But if more specialised work is required to extract and analyse the data, we can do it in France or another country," he added.
On Wednesday, Iran's Mehr news agency - close to ultraconservatives - quoted Mr Abedzadeh as saying Iran "would not give the black boxes to the Americans".
But the minister's statement on Thursday rejected "rumours of Iran's resistance to delivering the black boxes... to the US".
