A preliminary report by Iran's military said no evidence of foul play or attack had been found so far during investigations into the helicopter crash that killed President Ebrahim Raisi, state media reported on Friday.

Raisi, a hardliner who had been seen as a potential successor to Supreme Leader Ayatollah Ali Khamenei, was killed when his helicopter came down in poor weather in mountains near the Azerbaijan border on Monday.

"Signs of gunshot or similar were not observed in the wreckage of the helicopter (which) crashed in an area in high altitude and burst into flames," the report issued by the armed forces general staff said.

"Nothing suspicious has been observed in the control tower's conversations with the flight crew," it added. More details would be released as the investigation advanced, the report said.

Raisi was buried in the Shi'ite Muslim holy city of Mashhad on Thursday, four days after the crash that also killed Foreign Minister Hossein Amirabdollahian and six others.

Experts say Iran has a poor air safety record, with repeated crashes, many involving U.S.-built aircraft bought before the 1979 Islamic revolution.

Tehran says U.S. sanctions have long prevented it from buying new aircraft or spare parts from the West to update its creaking fleets.

Iran proclaimed five days of mourning for Raisi, who enacted Khamenei's policies, cracked down on public dissent and adopted a tough line on foreign policy issues including talks with Washington to revive Iran's 2015 nuclear pact.

A presidential election has been scheduled for June 28.

(Reporting by Dubai Newsroom; Editing by Andrew Heavens)