TEHRAN, Iran -- An official investigation into the helicopter crash in May that killed Iran's President Ebrahim Raisi and seven other people found it was caused by challenging climatic and atmospheric conditions, Iranian state TV reported Sunday.

The final report of the Supreme Board of the General Staff of the Armed Forces said the main cause of the helicopter crash was the complex climatic conditions of the region in spring, state TV said.

The report also cited the sudden appearance of a thick mass of dense fog rising upwards as the helicopter collided with the mountain.

According to the report, there were no signs of sabotage in parts and systems.

Raisi died alongside seven others including his foreign minister Hossein Amirabdollahian in the crash in a remote mountainous area in northwestern Iran.