DUBAI, August 21. /TASS/. Iranian agencies wrapped up an investigation into the death of Iranian President Ebrahim Raisi in a helicopter crash and determined that it was an accident, the Fars news agency reported, citing a source in one of the Iranian special services.

"The security and intelligence services completed an in-depth investigation and there is full confidence that what happened was an accident," he said.

"The helicopter with the president onboard was carrying two more persons than safety protocols permitted, so when the pilot noticed the fog and attempted to take the helicopter to the required altitude, the helicopter lacked the power to do so and, in the conditions of limited visibility due to the fog, a collision with a mountain took place," the source said.

Special services subjected at least 30,000 people to checks after Raisi's death, and concluded that human factor was not to blame, according to the source. He said the departure time had been set in advance, based on data from weather services, but the president's visit to the border with Azerbaijan ran over time, so by the time of departure the weather had worsened.

No GPS systems were installed on the helicopters in line with security requirements, the source said. That means the possibility of hacking the aircraft’s electronics systems and any attempts to tamper with them were ruled out.

The investigation also found no evidence of chemical or hazardous substances that could have caused the helicopter to crash.

On May 19, a helicopter carrying Raisi and other Iranian officials crashed in northern Iran. All passengers and crew members were killed.