However, Ukraine later withdrew a statement from the website of its Tehran embassy which ruled out terrorism or a missile strike.
Asked at a briefing in Kiev if the plane could have been downed by a missile, Ukraine’s Prime Minister Oleksiy Honcharuk cautioned against speculation until the results of an investigation were known.
He also said Ukraine had banned flights through Iranian airspace from January 9 and prosecutors have been ordered to open criminal proceedings over the crash.
The country’s President, Volodymyr Zelensky, said a team of experts had been sent to Iran to “establish the truth” about the deadly incident.
“Our priority is to establish the truth and those responsible for this terrible catastrophe,” he said.
Ukraine’s Foreign Minister said 82 Iranians, 63 Canadians, 11 Ukrainians and 10 Swedish nationals were on board the doomed flight. There were also four Afghans, three Germans and three Brits.
The plane, fully loaded with fuel for its 2300-kilometre flight, climbed to just short of 8,000 feet before it lost all communication with ground control.
It slammed into farmland near the town of Shahedshahr on the outskirts of Tehran. Videos taken immediately after the crash show blazes lighting up the darkened fields before dawn.
Iranian officials quickly claimed a mechanical fault was to blame and said one of the engines had failed and caught fire.
However experts have said the Boeing 737-800 aircraft was designed to keep flying if it lost an engine and suggested a potential “catastrophic” event had caused the airliner to plummet to the ground and burst into flames.
David Learmount told the UK Telegraph that the crew’s failure – or inability – to communicate with the ground had confused fellow aviation experts, “because the implication is that whatever happened was sudden and violent, forcing the crew immediately to fight for control”.
“Even a catastrophic engine failure – a possibility originally mooted by the Ukrainian authorities but then withdrawn – would be highly unlikely to have such a dramatic effect on control of the aircraft,” he said.
Ukraine International Airlines also cast doubt over claims of any engineering problems.
“It was one of the best planes we had, with an amazing, reliable crew,” the airline’s president Yevhen Dykhne said at a briefing.
The plane was built in 2016 and was last serviced just two days before the crash.
Qantas re-routes flights
Qantas and other major international airlines have been forced to re-route some flights to Europe as an emergency measure to avoid airspace around Iran following the overnight attack on Iraqi bases.
The standoff between the US and Iran threatens to hamper the investigation into the tragedy given Boeing, the plane’s manufacturer, is an American company.
Ali Abedzadeh, the head of Iran’s Civil Aviation Organisation, told the semi-official Mehr News Agency that the plane’s black boxes would not be handed to Boeing.
“We will not give the black box to the manufacturer and the Americans,” he said. “It is not clear at this time which country the black box is going to.”
US Secretary of State Mike Pompeo called for “complete cooperation” in any investigation.
“The United States will continue to follow this incident closely and stands prepared to offer Ukraine all possible assistance. The United States calls for complete cooperation with any investigation into the cause of the crash.”
Malaysia Airlines flight MH17 was shot down over Ukraine by a Russian-made Buk surface to air missile in 2015, killing all 298 passengers and crew members – including 38 Australians.
Four people allegedly responsible for the atrocity will go on trial in Amsterdam in March.
Bevan Shields is the Europe correspondent for The Sydney Morning Herald and The Age.