US forces carried out attacks on facilities belonging to an Iranian-backed militant Shi’ite group in Iraq on Sunday, in retaliation for a Friday strike on an American base that left a military contractor dead and four servicemen wounded, the Pentagon said in a statement.

The US strikes reportedly killed at least 12 Kataeb Hezbollah fighters.

“In response to repeated Kata’ib Hizbollah attacks on Iraqi bases that host Operation Inherent Resolve coalition forces, US forces have conducted precision defensive strikes against five KH facilities in Iraq and Syria that will degrade KH’s ability to conduct future attacks against OIR coalition forces,” Assistant to the Secretary of Defense Jonathan Hoffman said in a statement.

Operation Inherent Resolve is the name of the US mission against the Islamic State.

Hoffman said that among the five sites targeted by US forces were weapon storage facilities and command and control locations, two of which were in Syria, and blamed Kataeb Hezbollah for Friday’s rocket attack.

He added that the group “has a strong linkage with Iran’s Quds Force and has repeatedly received lethal aid and other support from Iran that it has used to attack OIR coalition forces.”

Sky News Arabic reported that one of the targets of the drone strikes was Kataeb Hezbollah’s main base near Al-Qaim, in the western Iraqi Anbar Province.

Hours after the American airstrikes, four rockets exploded near a base housing US troops close to Iraq’s capital, a security official said.

“Four Katyusha rockets exploded in the evening around the huge Taji Iraqi military base… which houses American soldiers, without causing casualties,” said the Iraqi official, who did not want to be named.

Attacks such as Friday’s and Sunday’s on US bases in Iraq have taken place on several occasions over the past few months, with American officials for the most part blaming Iran-backed fighters.

Iraq’s Kataeb Hezbollah, or the Hezbollah Brigades, a separate force from the Lebanese group Hezbollah, operates under the umbrella of the state-sanctioned militias known collectively as the Popular Mobilization Forces. Many of them are supported by Iran.

A senior member of the Popular Mobilization Forces, who spoke on condition of anonymity because he was not authorized to speak to the news media, said at least 12 fighters with Kataeb Hezbollah had died in US strikes along the Iraq and Syria border. His account could not immediately be independently confirmed.