A preliminary report by Iran’s military said no evidence of a criminal act or attack has been found so far in investigations into the helicopter crash that killed President Ebrahim Raisi, state media reported today.

Hardline Raishi, who was seen as a possible successor to Supreme Leader Ayatollah Ali Khamenei, was killed when the helicopter he was traveling in crashed in bad weather in the mountains near the border with Azerbaijan on Sunday.

“No evidence of gunfire or anything similar was observed in the wreckage of the helicopter which crashed in a high-altitude area and burst into flames,” said the report released by the general staff of the armed forces.

“Nothing suspicious has been observed in the control center’s conversations with the flight crew,” the text added. More details will be released as the investigation progresses, the report said.

Raishi was buried in the Shiite holy city of Mashhad yesterday, Thursday, four days after the helicopter crash that also killed Foreign Minister Hossein Amirabdollahian and six other people.

Experts say Iran has a poor aviation safety record, with repeated crashes of aircraft, many of them American-made, bought before the 1979 Islamic Revolution.

Tehran says US sanctions have long prevented it from buying new aircraft or spare parts from the West to modernize its fleet.

Iran declared five days of mourning for Raishi, who implemented Khamenei’s policies, suppressed public dissent and took a hard line on foreign policy including talks with Washington to revive the 2015 deal on Iran’s nuclear energy program.

The presidential election is scheduled to be held on June 28.