Iranian authorities today said that the Ukrainian airliner, which crashed shortly after takeoff from Tehran with the loss of all 176 people on board, had turned back after experiencing a problem.

Iranian Civil Aviation Organisation has said on its website that 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. It said the plane disappeared from radar screens the moment it reached 8,000 feet.

The pilot sent no radio message about the unusual circumstances. The organisation added that eyewitnesses have said, a fire was seen on board the plane which grew in intensity. The organisation said it has questioned witnesses both on the ground and on board a second aircraft which was flying above the Ukrainian Boeing 737 as the disaster unfolded.