There is growing speculation a jet that crashed near Tehran, killing 176 people, may have been accidentally - or deliberately - shot down by Iranian air defences.
The Boeing 737-800, operated by Ukraine International Airlines, had just taken off and was still climbing when disaster struck, with a fire appearing to take out one of the planes engines. Communication with the plane was lost and it changed direction slightly, before crashing into a field a few minutes later.
Ukraine's embassy in the Middle Eastern nation initially ruled out terrorism or a rocket strike, before rescinding the statement and saying it was too early to draw conclusions about what brought down flight 752.
The timing of the tragedy - just hours after Iran launched rockets at bases housing US troops in Iraq, and following a tweet by Iran's President referencing the shooting down of an Iranian airliner in 1988 - and Iran's reluctance to hand over the plane's black box recorder have led to speculation there's more to the story than just a technical fault.
Iran has no formal diplomatic relations with the US, where Boeing is based. Normally the country where the plane's manufacturer was based would be involved in any investigation.
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"We will not give the black box to the manufacturer and the Americans," Iran's Civil Aviation Organization head Ali Abedzadeh told a local news agency. "It's not yet clear which country the black box will go to for the investigation. This accident will be investigated by Iran's aviation organisation, but the Ukrainians can also be present during the incident's investigation."
The US has offered to cooperate, despite the escalation of tensions between the two nations in recent days.
The plane was only three years old, and had been serviced just before the crash, the airline said.
"It was one of the best planes we had, with an amazing, reliable crew," Ukraine International president Yevhen Dykhne said at a briefing.
"Planes just don't blow up in midair," aviation consultant Richard Aboulafia told the New York Times. "It doesn't work like that."
"Airplanes don't just catch fire and have that fire spread like that in such a short period of time, unless there was an intentional act causing that fire and explosion," Jeffrey Guzzetti, who used to head the US Federal Aviation administration's accident investigation division, told Bloomberg.
Even with one engine taken out, 737s can still fly just fine.
"Even a catastrophic engine failure would be highly unlikely to have such a dramatic effect on control of the aircraft," FlightGlobal's David Learmount told The Telegraph. "A 737 is capable of flying safely on just one of its two engines."
A US think tank, the Institute for Global Threats and Democracies Studies, claimed photos of the debris showed shrapnel damage consistent with the kind of damage seen on debris from Malaysia Airlines flight MH17, which was shot down over Ukraine a few years ago by Russian-backed separatists.
But fact-checking outlet Bellingcat said high-definition photographs suggested most of the 'holes' are actually just rocks and mud.
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Before launching rocket attacks in Iraq, President Rouhani tweeted a threat to the US, which in hindsight some have suggested might have been a preview of what was to come near Tehran.
"Those who refer to the number 52 should also remember the number 290. #IR655," he wrote. The 52 refers to the number of US hostages held at the US embassy in Tehran and the number of sites US President Donald Trump said would be hit if Iran retaliated against the killing of its high-ranking general, Qasem Soleimani.
The 290 and #IR655 refer to Iran Air Flight 655, a passenger service shot down by the US in 1988, killing 290 civilians. The US thought it was an Iranian F-14, but it turned out to be an Airbus A300. The US ended up having to pay compensation to Iran, but never admitted any legal liability for the deaths, which included 66 children.
