TEHRAN, – Two Iranian fighter jet pilots were killed Tuesday in an accident at a military airbase in the southwest of the country, state media reported.

The accident happened before the F-5 plane they were in took off from the base in Dezful, the city’s governor Ali Farahmandpour was quoted as saying by state news agency IRNA.

The airbase was closed off and the cause of the accident, initially described as “technical”, was being investigated, he added.

Farahmandpour said there was no “air accident or crash” and that further details on what happened would be made public after the investigation, according to state television’s website.

Iran’s armed forces still mainly use aircraft purchased before the country’s 1979 Islamic Revolution, with years of international sanctions making it increasingly difficult to purchase parts for maintenance.