TEHRAN -- The General Staff of Iran's Armed Forces on Thursday released the first report on the causes of a recent helicopter crash that resulted in the deaths of Iranian President Ebrahim Raisi and his entourage.

Following the crash, a senior investigation committee composed of experts, specialists and technicians arrived at the scene on Monday morning, the semi-official Tasnim news agency quoted the report by the General Staff of Iran's Armed Forces as saying.

According to the report, the helicopter had remained on its predetermined course all along the way and had not deviated from the flight route.

Almost one minute and a half before the incident, the pilot of the crashed helicopter had contacted the other two helicopters of the president's convoy, the report said.

No trace of bullets or similar items have been detected on the wreckage of the crashed helicopter, it said.

After crashing into the mountain, the helicopter had caught fire, it said.

"Complications of the region, fog and low temperature" had caused the search and rescue operations to continue until nightfall and then throughout the night, the report said, adding, "At 5:00 a.m. local time on Monday (0130 GMT), with the assistance of drones, the exact location of the incident was identified."

No suspicious issue had been detected in the conversations between the watchtower and the flight crew, it added.

More details would be provided after further investigations, it said.

Raisi and his entourage were en route to East Azarbaijan province when the helicopter carrying them crashed in a mountainous area on Sunday.

Also on board the helicopter were Foreign Minister Hossein Amir-Abdollahian and Mohammad Ali Ale-Hashem, the representative of Iran's Supreme Leader to East Azarbaijan.

Raisi was laid to rest on Thursday in the holy shrine of Imam Reza in his hometown, the northeastern city of Mashhad.