Three British nationals were on board the Ukrainian plane that crashed in Iran leaving no survivors, the Ukrainian foreign minister has said.
They were among the more than 170 people from seven countries on board the flight from Tehran to Kyiv.
Ukraine International Airlines flight PS752 crashed just after taking off from Imam Khomeini airport at 06:12 local time (02:42 GMT).
The plane underwent scheduled maintenance on Monday.
Among the victims were 82 Iranians, 63 Canadians, 11 Ukrainians – including all of the crew, 10 Swedes, four Afghans and three Germans, Vadym Prystaiko said.
Rescue teams have been sent to the crash site but the head of Iran’s Red Crescent told state media that it was “impossible” for anyone to have survived the crash.
Prime Minister Boris Johnson and Labour leader Jeremy Corbyn both said their thoughts were with the families of those killed as Prime Minister’s Questions got under way.
A UK Foreign Office spokesman has said: “We are deeply saddened by the loss of life in the plane crash in Iran overnight.”
They said it was “urgently seeking confirmation” about how many British nationals were on board and would be supporting any families affected.
Ukraine’s state aviation service has forbidden its national airlines from using Iranian airspace from Thursday, with the restrictions in place until an investigation into the cause of the crash has concluded.
Ukraine’s embassy in Tehran and Iranian state television both initially said technical issues caused the crash.
But the embassy later removed this statement and said any comment regarding the cause of the accident prior to a commission’s inquiry was not official.
Ukraine said its entire civilian aviation fleet would be checked for airworthiness and criminal proceedings would be opened into the disaster.
The country’s president warned against “speculation or unchecked theories regarding the catastrophe” until official reports were ready.
There was no sign of any problems with the plane before take-off and the airline’s president said it had an “excellent, reliable crew”.
Ukrainian International Airlines said its flight from Tehran to Kyiv disappeared from radar just a “few minutes” after take-off.
The Ukrainian national carrier said according to preliminary data there were 167 passengers and nine crew members on board but its staff were “clarifying the exact number”.
“The airline expresses its deepest condolences to the families of the victims of the air crash and will do everything possible to support the relatives of the victims,” a statement said.
The airline said the aircraft was built in 2016 and had its last scheduled maintenance on Monday.
It is investigating the cause of the crash.
A statement from Boeing said its “heartfelt thoughts” were with all those affected following the “tragic event”.
There are several thousand Boeing 737-800s in operation around the world which have completed tens of millions of flights. They have been involved in 10 incidents, including this crash, where at least one passenger was killed, aviation safety analyst Todd Curtis told the BBC.
This is the first time a Ukraine International Airlines plane has been involved in a fatal crash.