Canadian Prime Minister Justin Trudeau has said he has intelligence that indicates a passenger plane that crashed in Iran was shot down.
He described the crash as a “tragedy that not only shocked Canada, but the rest of the world”.
Mr Trudeau added: “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. This may well have been unintentional.
Iran denies the reports, with government spokesman Ali Rabiei describing it as a “psychological warfare against Iran”, according to state TV.
He added: “All those countries whose citizens were aboard the plane can send representatives and we urge Boeing to send its representative to join the process of investigating the black box”.
Mr Trudeau’s comments came after US officials said they were “confident” the passenger plane that came down in Tehran was shot down by an Iranian missile, with President Donald Trump saying “somebody could have made a mistake”.
One official said US satellites had detected the launch of two missiles shortly before the plane crashed, followed by evidence of an explosion, Reuters news agency reported.
Two other officials said Washington believed the downing of the Ukraine International Airlines plane was accidental.
All 176 people – including three British nationals – were killed in the crash. Downing Street has said that four of them were British nationals.
Many of the passengers had been heading for Canada.
Mr Trudeau also said Iran had indicated it will keep black boxes in Iran, but have told Ukraine’s president that its investigators will be granted access.
He said his government will not rest until it gets closure, transparency, accountability and justice, but that it is too soon to be “apportioning blame for the crash” or drawing any conclusions.
“Canada is working with its allies to ensure that an indepth investigation is conducted so that we can uncover the causes of this tragic crash,” he said.
Iran’s head of civil aviation has dismissed the idea the plane was hit by a missile as “impossible”.
But European security sources have told Sky News they believe the US assessment is “credible”.
In a news conference, Donald Trump said: “I have my suspicions – I don’t want to say that because other people have those suspicions also. It’s a tragic thing.
“But somebody could’ve made a mistake on the other side. It was flying in… not our system, it was nothing to do with us… it was flying in a pretty rough neighbourhood and somebody could’ve made a mistake.
“Some people think it was mechanical. I don’t think that’s even a question, personally.”
US Secretary of State Mike Pompeo condemned Iran’s missile attack in a call with Iraqi prime minister Adil Abdul-Mahdi on Thursday, according to the state department.
Mr Trump’s comments came almost immediately after Downing Street said it is looking into “very concerning” reports the plane had been hit by a missile.
Fears were sparked by a Ukrainian official, who raised the prospect of the jet possibly having been targeted by an anti-aircraft missile.
Sky News’ foreign editor Deborah Haynes said: “There was a lot of bemusement among aircraft experts about how a plane being flown by an experienced crew – a relatively new airliner, just three years old, and had just passed it’s safe to fly test… how that could have had such a catastrophic failure.”
Oleksiy Danilov, secretary of Ukraine’s Security Council, told Ukrainian media officials had four working theories regarding the crash, including a missile strike.
Ukrainian investigators have arrived in Iran and are awaiting permission to examine the crash site and look for missile fragments.
“A strike by a missile, possibly a Tor missile system, is among the main (theories), as information has surfaced on the internet about elements of a missile being found near the site of the crash,” Mr Danilov said.
Newsweek said a Pentagon official, a senior US intelligence official and an Iraqi intelligence official confirmed Mr Danilov’s comments, but the Pentagon has not yet publicly commented.
The Iranian military has disputed suggestions the airliner was brought down by a missile – something Downing Street previously said there was “no indication” of.
Following a call between Boris Johnson and Ukraine President Volodymyr Zelenskiy, the prime minister’s spokesman said there needs to be “a full credible and transparent investigation in what happened”.
He later said on Thursday there is now “a body of information that the flight was shot down by an Iranian surface-to-air missile”, adding, “this may as well have been unintentional.”
He continued: “The UK continues to call on all sides urgently to deescalate to reduce tensions in the region.”
Mr Danilov said the three other possible causes under consideration include a drone or “other flying object” crashing into the plane mid-air, an explosion on the plane “as a result of a terrorist attack” or an engine malfunction causing the engine to explode.
A preliminary report by Iran’s civil aviation authority, published on Thursday, said the crew did not make a radio call for help and were trying to turn back when it came down just outside Tehran airport.
Investigators also said that the plane was engulfed in fire before it crashed.
The crash caused a massive explosion when the plane hit the ground, likely because the aircraft had been fully loaded with fuel for the flight to the Ukrainian capital Kiev, the report said.
It also confirmed that both of the black boxes that contain data and cockpit communications had been recovered, though they had been damaged and some data was lost.
Ukraine has requested the UK’s help in the crash investigation.
Mr Johnson also spoke to Iranian President Hassan Rouhani by phone on Thursday morning in which he called for an “end to hostilities” in the Gulf following Iranian missiles being launched at US and coalition bases in Iraq on Wednesday in retaliation for the US assassination of top general Qassem Soleimani last Friday.