A Boeing passenger jet crashed in Iran early on January 8, hours after Tehran had launched a barrage of missiles at bases housing American troops in Iraq, in retaliation for the killing of commander Qasem Soleimani in a US strike.
All 176 on board the Ukraine International Airlines (UIA) flight PS752 -- mainly Iranian-Canadian dual nationals but also Ukrainians, Afghans, Britons and Swedes -- were killed.
Speculation immediately emerged that the juxtaposition of the timing of the Iranian reprisals against the United States and the plane crash was no coincidence.
Iran has vehemently excluded the possibility that the plane was shot down, but Western leaders have said they believe this was the most likely explanation.
- What happened to the plane? -
The Boeing 737-800NG for UIA's flight PS752 between Tehran and Kiev took off from Imam Khomeini International Airport at 6:12 am local time.
There was with no distress message from the pilot but it had begun to turn back for the airport, according to the Iranian Civil Aviation Organization, before crashing at 6:18 am.
The aircraft slammed into the ground near Sabashahr in the outskirts of Tehran, its report said.
According to the Flight Radar 24 monitoring site, there were 10 departures from the Tehran airport that day before the departure of PS752.
- What do Western leaders say? -
Prime Minister Justin Trudeau said Canada had intelligence from multiple sources "including our allies and our own intelligence" that indicated "the plane was shot down by an Iranian surface-to-air missile."
"This may well have been unintentional," Trudeau added. He was backed by other Western leaders including Dutch Premier Mark Rutte and NATO chief Jens Stoltenberg.
Using almost identical language, British Prime Minister Boris Johnson said there was "a body of information" suggesting the flight was shot down by an Iranian surface-to-air missile. "This may well have been unintentional," Johnson added.
US President Donald Trump said he had "suspicions" as "somebody could have made a mistake," adding that it was not "even a question" the plane suffered mechanical failure.
On Friday, US Secretary of State Mike Pompeo said the United States believed it was "likely" that an Iranian missile downed the airliner.
"We are going to let the investigation play out before we make a final determination," he said.
- What do images of the crash show? -
The New York Times said it had obtained and verified a video appearing to show a missile hitting a plane at night above the Tehran suburb of Parand, west of the airport.
According to The New York Times, which said it had also verified other videos, the aircraft flew back towards the airport ablaze before rapidly crashing.
It said the person may have started filming after seeing a previous missile streak across the sky.
The paper noted that Iran's air defence systems would have been on high alert for possible American retaliation in the hours after its strikes on Iraq.
The footage indicated those on the plane "likely faced horrifying final moments," the paper said.
- Have missile fragments been found? -
Unverified images posted on social media show remains of a Russian-made Tor M-1 missile.
Tehran had received 29 such air defence systems from Moscow under a $700 million contract signed in 2005.
The Bellingcat open source analytics website said the origin of such images has yet to be determined, and the people who took the images have not come forward.
Experts have said the fact the plane did not explode immediately on impact does not contradict the theory it was hit by a missile.
"At that altitude, the aircraft is still not pressurised, and holes can be pierced in the cabin without it exploding. What causes an explosion is the pressurisation," said a French expert on missiles who asked not to be identified by name.
The expert said such a system is designed to explode as soon as it comes into proximity with a metallic surface, meaning a target should be left pockmarked with fragments of shrapnel.
- What is Iran's version? -
Iran has so far refused to countenance any suggestion that the plane was brought down by one of its missiles.
The country's civil aviation chief Ali Abedzadeh said that one "thing is for certain, this airplane was not hit by a missile," arguing that it would have exploded immediately.
And "the debris collected has been in a very limited area. If there was an explosion in the wings it should have been much more scattered," Abedzadeh said.
- What does Ukraine conclude? -
Ukrainian President Volodymyr Zelensky has so far been more circumspect than his Western counterparts on pinpointing a missile as the likely cause of the crash.
He said Friday that the possibility a missile struck the plane had not been ruled out, but had not yet been confirmed, the presidency said.
Ukrainian Foreign Minister Vadym Prystaiko said Friday that he and Zelensky had met US representatives and "received important data which will be processed by our experts."
He added Ukraine had been given access to the plane's black boxes.