BAGHDAD, June 26 (Reuters) -

Iraqi security forces raided a headquarters belonging to a powerful Iran-backed militia south of Baghdad late on Thursday, seized rockets and detained three commanders of the group at the site, two Iraqi government officials said.

The officials said the militia group targeted was the Iran-backed Kataib Hezbollah, which U.S. officials have accused of firing rockets at bases hosting U.S. troops and other facilities in Iraq.

Iraq's new prime minister, Mustafa al-Kadhimi, has indicated he will be tough on militia groups which target U.S. 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 U.S. embassy in Baghdad and other U.S. 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 leaders detained in the raid was an Iranian. Iraqi special forces from the Counter Terrorism Service carried out the raid, he said.

The official said the three detained leaders were handed over to the U.S. military. A spokesman for the U.S.-led coalition in Iraq said he "doubted" that Iraqi authorities had handed over the detainees.

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.