A Ukrainian airliner crashed soon after taking off from Tehran's Imam Khomeini airport on Wednesday, killing all 176 people aboard, Iran's state television and Ukraine's leaders said.
The Boeing 737 belonging to Ukraine International Airlines (UIA) crashed near the airport and burst into flames. Iranian TV said the crash was due to technical problems but did not elaborate.
Iranian state media later reported the Ukranian jet did not declare an emergency, quoting Iran Civil Aviation Organization official Hassan Rezaeifar - the general director of the body's panel to investigate aircraft accidents.
Ukraine President Volodymyr Zelenskiy said there were no survivors.
"My sincere condolences to the relatives and friends of all passengers and crew," Zelenskiy said in a statement, adding that Ukraine was seeking to establish the circumstances of the crash and the death toll.
Iranian state TV and Ukraine's prime minister said 167 passengers and 9 crew were on board. Iranian TV said 32 of those on board were foreigners.
Iranian media quoted an Iranian aviation official as saying the pilot of the airliner did not declare an emergency.
There was no official word from Ukraine International Airlines.
"The fire is so heavy that we cannot (do) any rescue... we have 22 ambulances, four bus ambulances and a helicopter at the site," Pirhossein Koulivand, head of Iran's emergency services, told Iranian state television.
Television footage showed debris and smoldering engine parts were strewn across a field, and rescue workers with face masks retrieving bodies of the victims.
According to air tracking service FlightRadar24, the plane that crashed was Flight PS 752 and was flying to Kyiv. The plane was three years old and was a Boeing 737-NG, it said.
A spokesman for Boeing said the company was aware of media reports of a plane crash in Iran and was gathering more information. The plane manufacturer grounded its 737 MAX fleet in March after two crashes that killed 346 people.
It was the first fatal crash for the Kyiv-based UIA.
Founded in 1992 after the collapse of the Soviet Union, planes operated by loss-making privately-held UIA, which is based out of Kyiv's Boryspil airport, had suffered technical problems in flight over the years but had never crashed before.
UIA says on its website it had been awarded the IOSA - the IATA Operational Safety Audit certificate - meaning its operational and safety standards were fully in line with international requirements.
The airline, which operates domestic and international flights, has a fleet of 42 planes made up, according to its own website, of various Boeings, including 737-800s and 737-900s. It also operates Embraer aircraft.
Financial problems forced it to scale back its route network last year.
UIA is in the process of trying to modernize its fleet and has ordered three Boeing 737 MAX aircraft which has not yet taken delivery of due to continuing safety concerns over the MAX project.