A Boeing 737 airliner from Ukraine International Airlines crashed shortly after take-off from Tehran early on Wednesday, bursting into flames and killing all 176 people on board.
Debris and smouldering engine parts from the aircraft, which Ukraine International Airlines said was last serviced two days ago, were strewn across a field southwest of the Iranian capital where rescue workers in face masks laid out scores of body bags.
Among the victims were 82 from Iran, 63 Canadians, 11 Ukrainians, 10 Swedes, three Germans and three Britons, Ukrainian Foreign Minister Vadym Prystaiko said.
The accident occurred as confrontation between Iran and the United States threatens to trigger a wider conflict in the Middle East, but officials cautioned that speculation about the cause of the crash was premature.
It was the Kyiv-based carrier's first fatal accident, and it said it was doing everything possible to establish what had happened.
Under international rules, responsibility for investigating the crash lies with Iran, and Iranian state television said both of the plane's black boxes had been found.
An amateur video, run by Iranian news agencies and purportedly of the crashed plane, showed a flash in the sky descending rapidly with comments that the aircraft was "on fire," followed by a larger flash as it appears to hit the ground. Reuters could not independently authenticate the footage.
Asked at a briefing in Kyiv if the plane could have been downed by a missile, Ukraine's Prime Minister Oleksiy Honcharuk cautioned against speculation until the results of the investigation were known.
Relations between Washington and Tehran are in crisis, with Iran having launched missiles at bases housing US forces in Iraq several hours before the plane crash, in retaliation for a US drone strike last week that killed a top Iranian military commander.
Major airlines canceled Iran and Iraq flights and re-routed others away from both countries' airspace following the Iranian missile strikes.
In Paris, the maker of the plane's engines, French-US firm CFM — co-owned by General Electric and France’s Safran — said any speculation regarding the cause was premature.
Safety experts say airliner accidents are rarely triggered by a single cause and that it typically takes months of investigation to understand all the factors behind them.
An official at Ukraine's embassy in Tehran said Iranian authorities had asked it to rescind an initial statement from Iran based on preliminary information that had blamed the accident on engine failure.
Iranian TV said the crash was due to unspecified technical problems, and Iranian media quoted a local aviation official as saying the pilot did not declare an emergency.
Offering "sincere condolences" to relatives of victims, Ukraine President Volodymyr Zelenskiy said he had instructed his prosecutor general to open criminal proceedings following the crash, without specifying who they would involve.
Ukraine would test the airworthiness of its entire civilian fleet of aircraft, he added.
Good safety record
The plane that crashed was a three-year-old Boeing 737-800NG en route to Kyiv. Its last scheduled maintenance was on Jan. 6, the airline said.
A spokesman for the manufacturer said it was gathering more information.
"We are in contact with our airline customer and stand by them in this difficult time. We are ready to assist in any way needed," the company said in a later statement.
The 737-800 is one of the world’s most-flown models with a good safety record and does not have the software feature implicated in crashes of the 737 MAX. Boeing grounded its 737 MAX fleet in March after two crashes that killed 346 people.
Modern aircraft are designed and certified to cope with an engine failure shortly after take-off and to fly for extended periods on one engine. However, an uncontained engine failure releasing shrapnel can cause damage to other aircraft systems.
Under international rules, Ukraine would be involved in the investigation into Wednesday's crash, and the United States would usually be accredited as the country where the jet was designed and built. France, where engine maker CFM has half its activities, may also be involved.
There was no immediate word on whether the US National Transportation Safety Board would be involved. The NTSB usually invites Boeing to give technical advice in such investigations.