TEHRAN - The plane that crashed in Iran killing all 176 people on board was trying to return to the airport at the time of the incident, Iranian investigators have said.
The Boeing 737-800 crashed minutes after taking off from Tehran airport, with an initial investigation suspecting that it caught fire in the air as it was leaving the airport zone.
The crash came shortly after Tehran launched missiles at US forces in Iraq in response to the killing of a top Iranian general in a US drone strike in Baghdad.
However, there is yet no evidence that the two events are linked.
Both Canada and the United States called for a full investigation to determine the cause.
Oleksiy Danylov, the secretary of Ukraine’s security council, said Thursday that investigators would scour the crash site for any signs of missile debris, although Iran is known to have Russian missile defence systems.
"The plane, which was initially headed west to leave the airport zone, turned right following a problem and was headed back to the airport at the moment of the crash," the Iranian Civil Aviation Organisation said on its website late Wednesday.
"The plane disappeared from radar screens the moment it reached 8,000 feet (2,400 metres). The pilot sent no radio message about the unusual circumstances.
"According to eyewitnesses, a fire was seen on board the plane which grew in intensity," the organisation added, reporting the first findings of its investigation into the crash.
The organisation said it had questioned witnesses both on the ground and on board a second aircraft which was flying above the Ukrainian Boeing 737 as the disaster unfolded.
Ukraine's Tehran embassy initially blamed engine failure but later removed the statement, saying any comment regarding the cause of the accident prior to a commission's inquiry was not official.
According to Ukraine, 82 Iranians, 63 Canadians, 10 Swedes, four Afghans, three Germans and three Britons were on board, as well as 11 Ukrainians, including nine crew.
About 30 came from the Iranian community around Edmonton, capital of Alberta province in western Canada, where resident Payman Parseyan described the tragedy as “devastating".
Debris and body bags lined the floor of the crash site, including luggage and a Santa doll.
Given that the plane was an American-made Boeing 737, the US National Transportation Safety Board would normally have a role to play in investigations, in accordance with legislation of the country where the crash took place.
However, Iran’s civil aviation chief, Ali Abedzadeh, said Iran would cooperate with Ukraine, but not send the black boxes to the United States, with which it has no diplomatic relations.
He added that it was not yet clear who would analyse the cockpit voice recorder and the flight data recorder that make up the black boxes.
According to aviation experts, only a handful of countries are capable of analysing black boxes, notably Britain, France, Germany and the United States.
Boeing said the plane was built in 2016 and checked only two days before the tragedy, UIA’s first fatal crash, and that it was ‘ready to assist in any way needed’.