An explosion took place at an Iranian gas storage facility in an area which houses a sensitive military site near the capital Tehran, a defense ministry spokesman told state TV on Friday.
The explosion took place in the "public area" of Parchin, said the spokesman, Davoud Abdi, as opposed to the military site, where Western security services believe Tehran carried out tests relevant to nuclear bomb detonations more than a decade ago. Iran has denied this.
Abdi said the fire was brought under control and there were no casualties. He did not give any information about the cause of the blast.
Videos and pictures posted on social media that were picked up by local news outlets showed an explosion with a bright orange flash, followed by a large plume of smoke.
Meanwhile,Iraqi security forces raided a headquarters belonging to a powerful Iran-backed militia in southern Baghdad late on Thursday, seized rockets and detained three commanders of the group, two Iraqi government officials said.
The officials said the militia group targeted was the Iran-backed Kataib Hezbollah, which US officials have accused of firing rockets at bases hosting US troops and other facilities in Iraq.
It was the most brazen raid in years by Iraqi security forces against a powerful paramilitary group backed by Tehran, whose proxy militias have developed military, political and economic dominance in Iraq.
Iraq's new prime minister, Mustafa al-Kadhimi, has indicated he will be tough on militia groups which target US installations. The raid, which took place after midnight, is the first sign Kadhimi will follow through on his tough talk.
It took place after a number of rocket attacks near the US embassy in Baghdad and other US military sites in the country in recent weeks.
There was no immediate comment from Iraqi militia groups or from Iran. Both Tehran and Washington supported Kadhimi in becoming prime minister in May.
One of the government officials told Reuters one of the three commanders detained in the raid was an Iranian. Iraqi special forces from the Counter Terrorism Service carried out the raid, he said.
A spokesman for the US-led coalition in Iraq and Iraqi paramilitary sources denied an earlier statement by one of the government officials that the commanders detained were handed over to the US military.
The official said the three detained commanders were handed over to the US military. The Iraqi official said at least 20 other fighters were detained during the raid.
Tensions between Washington and Tehran especially on Iraqi soil have been high for at least a year.
It nearly spilled into regional conflict in January after the United States killed Iran's military mastermind Qassem Soleimani and Iraqi paramilitary chief Abu Mahdi al-Muhandis in a drone strike at Baghdad airport.