A Ukrainian airliner carrying 176 people from seven countries crashed shortly after takeoff from Tehran on Wednesday, killing all on board.
The vast majority of the passengers on the Boeing 737 flight from Tehran to Kiev were non-Ukrainians, including 82 Iranians and 63 Canadians, officials said.
The crash occurred with tensions high in the Middle East and shortly after Tehran launched missiles at bases in Iraq housing US troops. But there was no immediate indication of foul play and Ukrainian President Volodymyr Zelensky warned against "speculating" on the cause of the disaster.
The US aviation authority said it had banned US-registered carriers from flying over Iraq, Iran and the Gulf, and airlines including Lufthansa and Air France said they were suspending flights through Iraqi and Iranian airspace.
Footage released by Iranian state media showed a field on fire and the smoking wreckage of the crash. Rescue workers carried body bags and the passengers' personal items -- including cases, clothes, a Santa Claus doll and a boxing glove -- were lying amidst the debris.
Ukraine International Airlines (UIA), the ex-Soviet country's privately owned flagship carrier, said flight PS752 took off from Tehran airport at 6:10 am and disappeared from radars just two minutes later.
It slammed into farmland at Khalaj Abad, in Shahriar county, about 45 kilometres (30 miles) northwest of the airport, according to reports on Iranian state media.
Officials in both Iran and Ukraine said there was no hope of anyone having survived.
As well as the Iranians and Canadians, the passengers included 10 Swedes, four Afghans, three Germans and three Britons, Ukraine's foreign minister said. Eleven Ukrainians -- including the nine crew -- were also on board.
Canada is home to a large Iranian diaspora community and UIA offers discount flights between Tehran and Toronto, with a transit in Kiev.
Officials in Tehran said 15 children were among the passengers. The semi-official news agency ISNA said 13 were students from Tehran's Sharif University, the most prestigious in the country.
The airline -- which suspended its flights to Tehran after the crash -- said the Boeing 737 had been built in 2016 and checked only two days before the accident.
"The plane was in working order," UIA company president Yevgeniy Dykhne told a briefing in Kiev where he choked back tears. "It was one of our best planes with a wonderful crew."
Zelensky, who cut short a vacation to Oman to return to Kiev, ordered an investigation into the crash and a sweeping check of "all civilian aircraft" in the country.
"I ask everyone to keep from speculating and putting forth unconfirmed theories about the crash," Zelensky wrote on Facebook.
Iranian state media reported that the plane caught fire after crashing, but a video aired by the state broadcaster appeared to show the plane already on fire as it fell from the night sky.
Iran on Wednesday fired more than a dozen ballistic missiles at Iraqi bases housing the US military, in the first action of its promised revenge for the US killing of a top Iranian general.
"There is a lot of speculation at the moment it has been shot down -- I think that is not going to be the case at all," said Stephen Wright, a professor of aircraft systems at Tampere University in Finland.
"The aircraft was climbing... it was going up in the right direction, which means that something catastrophic has happened.
"It could be a bomb or it could be some sort of catastrophic breakup of the aircraft."
The aircraft was not one of the MAX models fitted with anti-stall systems that have been linked with two other recent crashes of Boeing 737s.
Boeing, which has been roiled by a nine-month crisis after 737 MAX was grounded, tweeted on Wednesday: "We are aware of the media reports out of Iran and we are gathering more information."
UIA vice president Igor Sosnovskiy told reporters in Kiev that the airline doubted its crew was at fault.
"(The chances) of a crew error are minimal, we simply are not considering them," he said. "Considering their experience, it's difficult to say that there was something wrong with the crew."
The airline was notifying passengers' families and working with aviation authorities "to do everything possible to find the reasons for the aviation accident," he said.
A statement posted on the website of the Ukrainian embassy saying the crash was caused by an engine malfunction and ruling out an act of terror was later redacted, saying all information will now be provided by an official commission.
Iran's civil aviation authority said search and rescue teams had found the airliner's two black boxes.
The Red Crescent in Iran said its teams were being assisted by soldiers and firefighters in the effort to recover bodies.
"All operational teams were dispatched to the area," Shahin Fathi, the head of its search and rescue unit, told state television. "Unfortunately... we haven't found anyone alive."