People stand near the wreckage of a Ukraine International Airlines plane that crashed near Imam Khomeini airport in Tehran on Wednesday. All 167 passengers and nine crew were killed when it crashed shortly after taking off on Wednesday, Iranian state media reported. Photo: AFP

Iranian authorities have said a Ukrainian airliner, which crashed outside Tehran with the loss of all 176 people on board, had turned back after suffering a problem, as Ukrainian experts joined the investigation on Thursday.

Both Canada and the US called for a full investigation to determine the cause of Wednesday's crash, which 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.

There was no immediate indication that foul play may have caused the Ukraine International Airlines plane to go down soon after take-off.

"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 Organization said on its website late Wednesday.

"The plane disappeared from radar screens the moment it reached 8,000 feet [2,400 meters]. The pilot sent no ­radio message about the unusual circumstances."

Investigators are pursuing several leads following the crash, including a surface-to-air missile strike, an act of terror and engine failure, a Ukrainian security official said on Thursday.

"For the moment we are working on seven different versions of the event that took place in Iran," Oleksiy Danilov, the secretary of Ukraine's national security and defense council , told AFP.

Danilov also said on Facebook that the leads being studied include both technical malfunctions and foul play, but told AFP that "there is no priority version" yet.

The leads under consideration include a collision with another airborne object, a rocket from Iran's missile defense system, an engine explosion caused by a technical problem, and an explosion on board the aircraft due to an "act of terror," he said on Facebook.

Danilov told AFP that for the moment there was no reason to believe that the airliner had been hit by a missile.