Iranian President Ebrahim Raisi died in a helicopter crash in northwest Iran on Sunday.
The crash involved a US-manufactured Bell 212 helicopter, which stopped being made in 1998.
Iran's former foreign minister said US aircraft sanctions against Iran could be to blame.
Raisi, 63, and other senior officials were killed after the helicopter they were traveling in was forced to make a "hard landing" over northwest Iran, Ahmad Vahidi, the country's interior minister, told IRNA.
State TV said the helicopter crashed into a mountain. While there is no official statement on the cause, images of the crash site captured by ISNA, Iran's state students' news agency, showed heavy fog lingering over the area.
Multiple outlets, including Reuters, said the helicopter was a US-manufactured Bell 212, a model that first entered service in 1968 and stopped being made in 1998.
Iran's former foreign minister, Mohammad Javad Zarif, said the US sanctions - which prohibit Iran from purchasing US-built aircraft - could be partly to blame.
In a phone interview with state TV on Monday, Zarif said the sanctions prevent Iran from having good aviation facilities.
According to part of an interview cited by Iran International and ISNA News Agency, he said the crash that killed Raisi would be "recorded in the black list of American crimes against the Iranian nation."
The US has imposed various sanctions against Iran since the seizure of the US Embassy in Tehran in 1979. Economic sanctions, including those targeting the aviation industry, were reinstated in 2018 after the US withdrew from its nuclear deal.
According to the Washington Institute, a US think tank, Iranian airlines are prohibited from purchasing aircraft that contain more than 10% US parts.
This is likely to complicate the process of updating or repairing US-manufactured aircraft that the country purchased before the sanctions took effect.
Iranian airlines operate some of the world's oldest aircraft, according to Bloomberg, which estimated the average fleet age to be over 25 years.
According to US military training documents cited by Reuters, the Bell 212 was developed for the Canadian military in the late 1960s and first used by Canada and the US in 1971.
There have been multiple crashes involving a Bell 212 through the years, including a 1997 crash in Louisiana where eight people died, according to First Post.
In 2009, a Bell 212 operated by Cougar Helicopters crashed off the coast of Newfoundland in Canada. The incident, which killed 17 of the 18 people on board, was a result of an emergency landing after the aircraft lost oil pressure in one of its engines, First Post said.
The most recent fatal crash involving a Bell 212 took place in September when a private aircraft crashed off the coast of the United Arab Emirates, according to the nonprofit Flight Safety Foundation, cited by Reuters. It is not known how many passengers were on board.
Iran's Ministry of Foreign Affairs did not immediately respond to a request for comment.
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