US Secretary of Defense Lloyd Austin says US forces have attacked facilities in Iraq used by Iran-backed militant groups in retaliation of their raids against US troops.

Austin said in a statement on Monday that "US military forces conducted necessary and proportionate strikes on three facilities used by Kataib Hezbollah and affiliated groups in Iraq."

He said, "These precision strikes are a response to a series of attacks against US personnel in Iraq and Syria by Iranian-sponsored militias."

Austin said three US personnel were wounded in an attack by the groups on the US Erbil Air Base in Iraq on Monday and that one of them was in critical condition.

He said he "will not hesitate to take necessary action to defend the United States, our troops, and our interests."

White House National Security Council spokesperson Adrienne Watson said in a statement on Monday that "US military personnel were targeted by a one-way attack drone" in northern Iraq earlier on Monday.

Iran-backed militia groups have been attacking US bases in Iraq since the latest bout of violence started between Israel and the Palestinian Islamic group of Hamas.

The militias said on social media on Monday that their drone attacked the US base to show resistance to the stationing in Iraq of what they call US occupation forces and retaliation for killings in the Gaza Strip by Israel. They vow to continue their attacks on US forces.