A Ukrainian airliner carrying 176 people crashed on Wednesday due to technical problems soon after taking off from Tehran's Imam Khomeini airport, and all aboard were killed, Iran's state television and Ukraine's leaders said.
The Boeing 737 belonging to Ukraine International Airlines crashed near the airport and burst into flames.
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.
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 smouldering engine parts 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 Kiev. 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.
FAA bans airlines from flying over Iraq, Iran
Meanwhile the US Federal Aviation Administration said it would ban US carriers from operating in the airspace over Iraq, Iran, the Gulf of Oman and the waters between Iran and Saudi Arabia after Iran launched a missile attack on US-led forces in Iraq.
Tehran fired more than a dozen ballistic missiles from Iranian territory against at least two Iraqi military bases hosting US-led coalition personnel, the US military said on Tuesday.
The FAA said it issued the airspace ban "due to heightened military activities and increased political tensions in the Middle East, which present an inadvertent risk to US civil aviation operations."
Several non-US airlines had flights over parts of Iraq and Iran at the time, according to FlightRadar24 data. They are not directly affected by the FAA ban, but foreign carriers and their national regulators typically consider US advice carefully when deciding where to fly.
Before the latest guidance, the FAA had already prohibited US carriers from flying below 26,000 feet over Iraq and from flying over an area of Iranian airspace above the Gulf and Gulf of Oman since Iran shot down a high-altitude US drone last June.
Singapore Airlines Ltd said after the attack on US bases in Iraq that all of its flights would be diverted from Iranian airspace.
Carriers are increasingly taking steps to limit threats to their planes after Malaysia Airlines Flight MH17 was shot down in 2014 by a missile over Ukraine, killing all 298 people on board. Re-routing around conflict airspace adds to flight times and burns extra fuel.
Korean Air Lines Co Ltd said it had been avoiding Iranian and Iraqi airspace before the attack on US troops.
OPSGROUP, which advises airlines on security threats, said the new US airspace bans were "significant", particularly given that the entire overwater airspace in the region is now unavailable.
"Flights headed to/from the main airports in the region such as Dubai will now need to route through Saudi Arabia's airspace," it said on its website.
