WASHINGTON (AP) President Joe Biden ordered the United States military to carry out retaliatory airstrikes against Iranian-backed militia groups after three U.S. service members were injured in a drone attack in northern Iraq.

National Security Council spokesperson Adrienne Watson said one of the U.S. troops suffered critical injuries in the attack that occurred earlier Monday. The Iranian-backed militia Kataib Hezbollah and affiliated groups, under an umbrella of Iranian-backed militants, claimed credit for the attack that utilized a one-way attack drone.

Iraqi officials said U.S. strikes targeting militia sites early Tuesday killed one militant and injured 18. They came at a time of heightened fears of a regional spillover of the Israel-Hamas war.

Iran announced Monday that an Israeli strike on the outskirts of the Syrian capital of Damascus killed one of its top generals , Razi Mousavi, who had been a close companion of Gen. Qassem Soleimani, the former head of Irans elite Quds Force. Soleimani was slain in a U.S. drone strike in Iraq in January 2020.

Iranian officials vowed revenge for the killing of Mousavi but did not immediately launch a retaliatory strike. The militia attack Monday in northern Iraq was launched prior to the strike in Syria that killed Mousavi.

Biden, who was spending Christmas at the presidential retreat at Camp David, Maryland, was alerted about the attack by White House national security adviser Jake Sullivan shortly after it occurred Monday and ordered the Pentagon and his top national security aides to prepare response options to the attack on an air base used by American troops in Irbil.

Sullivan consulted with Defense Secretary Lloyd Austin . Bidens deputy national security adviser, Jon Finer, was with the president at Camp David and convened top aides to review options, according to a U.S. official, who was not authorized to comment publicly and requested anonymity.