Rescue teams work amidst debris after a Ukrainian plane carrying 176 passengers crashed near Imam Khomeini airport in the Iranian capital Tehran early in the morning on January 8, 2020, killing everyone on board.

A Ukrainian International Airlines plane that crashed shortly after leaving Tehran on Wednesday, killing all 176 people on board, was reportedly on fire before impact, according to Iran's civil aviation authority.

Ali Abedzadeh, head of the National Aviation Authority, said in a statement that eyewitnesses had reported that the Kyiv-bound Boeing 737-800 plane was on fire immediately before the crash.

The plane's trajectory indicated it was initially heading westward, turning right after the problem and was on its way back to a nearby airport at the time of the crash, Abedzadeh said.

He said no radio messages were received by the pilot regarding unusual circumstances. The aircraft had risen to an altitude of 8,000 feet after taking off from the Imam Khomeini Airport before disappearing from radar, he added.

The loss of the Ukrainian International Airlines Flight 752 occurred amid heightened tensions and open hostilities between the U.S. and Iran and the reasons for the plane's crash are under greater scrutiny.

Reuters reported, citing five anonymous security sources, that Western intelligence agencies believe the plane had suffered a technical malfunction and not been brought down by a missile.

Under international law, the country where the crash occurred controls the investigation and there have been reports Iran has refused to hand over the black box flight recorders to Boeing or U.S. aviation authorities — agencies that would usually participate in an investigation into a crash of a U.S.-manufactured plane.