The cause of the explosions has not yet been determined, Fars quoted local sources as saying.

According to Fars, the explosions were heard in Qahjavarestan city, near Isfahan's International Airport and an Iranian army air force base, Xinhua news agency reported.

Meanwhile, Iran's official IRNA news agency, citing the Iran Airports and Air Navigation Company, reported that all flights in airports in several Iranian cities, including Tehran, Isfahan and Shiraz, were suspended due to security reasons.

IRNA added that Iran activated its air defence system over several cities on Friday.