Air strikes targetted Iraq's Popular Mobilization Forces umbrella grouping of Iran-backed Shi'ite militias near camp Taji north of Baghdad.
Four Katyusha rockets hit a base on Sunday that houses U.S. troops near the Iraqi capital Baghdad, an Interior Ministry official said.
The incident took place in the evening when the rockets struck al-Taji military base, some 30 kilometers north of Baghdad, the official told Xinhua on condition of anonymity.
There were no immediate reports about casualties, the official told the Chinese media.
An Iraqi army source said that the strike had killed six people and critically wounded three, reported Reuters. Two of the three vehicles making up a militia convoy were found burned, the source said, as well as six burned corpses. The strikes took place at 1:12 am local time, he said.
The attack came a few hours after the U.S. forces attacked five bases of Kata'ib Hezbollah (KH) in Iraq and Syria in response to repeated attacks by KH against U.S.-led coalition forces in Iraq, according to a U.S. military statement.
The U.S. forces targeted three KH bases in Iraq and two in Syria, the statement said, adding that "these locations included weapon storage facilities and command and control locations that KH uses to plan and execute attacks on coalition forces."
According to a statement by the media office affiliated with the Iraqi Joint Operations Command (JOC), three U.S. airstrikes targeted headquarters of Hashd Shaabi's 45th Brigade near al-Qaim border town with Syria.
The airstrikes left four Hashd Shaabi members killed, including the deputy commander of the 45th Brigade, and some 30 others wounded, the statement said citing initial reports.
The statement gave no further detail but said that more information will be released later.
The attack came two days after a rocket barrage hit K1 military camp, which houses U.S. troops, in Kirkuk province, leaving a U.S. contractor killed and wounding others.
Military bases housing U.S. troops across Iraq and the heavily fortified Green Zone in central Baghdad have been frequently targeted by insurgents' mortar and rocket attacks.
On Dec. 14, the U.S. embassy in Iraq accused in a statement Iran's proxies of carrying out attacks on Iraqi military bases where U.S. troops are stationed.
Over 5,000 U.S. troops have been deployed in Iraq to support the Iraqi forces in the battles against Islamic State (IS) militants, mainly providing training and advising to the Iraqi forces.
The troops are part of the U.S.-led international coalition that has been conducting air raids against IS targets in both Iraq and Syria.