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

National Security Council spokesperson Adrienne Watson said one of the US troops suffered critical injuries in the attack that occurred 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 that US strikes targeting militia sites early Tuesday killed one fighter and wounded 18. They came at a time of heightened fears of a regional spillover of the Israel-Hamas war.

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

Iranian officials vowed revenge for the killing of Mousavi, but didn’t immediately launch a retaliatory strike.

The militia attack on US forces on Monday in northern Iraq was launched prior to the alleged Israeli strike in Syria that killed Mousavi.

Biden, who was spending Christmas at the presidential retreat at Camp David, Maryland, was alerted to the Iraq 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 Erbil.

Sullivan consulted with US Defense Secretary Lloyd Austin. Biden’s deputy national security adviser, Jon Finer, was with the president at Camp David and convened top aides to review options, according to a US official, who wasn’t authorized to comment publicly and requested anonymity.

Within hours, Biden convened his national security team for a call in which Austin and Gen. CQ Brown, chair of the Joint Chiefs of Staff, briefed Biden on the response options.

Biden opted to target three locations used by Kataib Hezbollah and affiliated groups, the official said. The US strikes were carried out at about 4:45 a.m. Tuesday in Iraq, less than 13 hours after the US personnel were attacked.

According to US Central Command, the retaliatory strikes on the three sites “destroyed the targeted facilities and likely killed a number of Kataib Hezbollah militants.”

“The President places no higher priority than the protection of American personnel serving in harm’s way,” Watson said. “The United States will act at a time and in a manner of our choosing should these attacks continue.”

The latest attack on US troops follows months of escalating threats and actions against American forces in the region since the devastating October 7 Hamas attack that sparked the war in Gaza.

Israel launched its offensive after the terror group led an unprecedented assault into southern Israel. Some 1,200 people in Israel, most of them civilians, were massacred. Another approximately 240 people were kidnapped.

The back-and-forth strikes between the US and Iran have escalated since Iranian-backed militant groups under the umbrella group called the Islamic Resistance in Iraq and Syria began striking US facilities October 17.

Iranian-backed militias have carried out more than 100 attacks on US bases in Iraq and Syria since October 7.

In November, US fighter jets struck a Kataib Hezbollah operations center and command and control node, following a short-range ballistic missile attack on US forces at Al-Assad Air Base in western Iraq. Iranian-backed militias also carried out a drone attack at the same air base in October, causing minor injuries.

The US has also blamed Iran, which has funded and trained the Hamas terror group, for attacks by Yemen’s Houthis against commercial and military vessels through a critical shipping choke point in the Red Sea. The Houthis have also launched a number of drone and missile attacks on Israel.

The Biden administration has sought to prevent the Israel-Hamas war from spiraling into a wider regional conflict that either opens up new fronts of Israeli fighting or draws the US in directly. The administration’s measured response — where not every attempt on American troops has been met with a counterattack — has drawn criticism from Republicans.

The US has thousands of troops in Iraq training Iraqi forces and combating remnants of the Islamic State group, and hundreds in Syria, mostly on the counter-IS mission. They have come under dozens of attacks, though as yet none fatal, since the war began on October 7, with the US attributing responsibility to Iran-backed groups.

“While we do not seek to escalate conflict in the region, we are committed and fully prepared to take further necessary measures to protect our people and our facilities,” Austin said in a statement.

The clashes put the government of Iraqi Prime Minister Mohammed Shia al-Sudani in a delicate position. He came to power in 2022 with the backing of a coalition of Iranian-backed parties, some of which are associated with the same militias launching the attacks on US bases.

A group of Iranian-backed militias known as the Popular Mobilization Forces were key in the fight against Islamic State militants after the extremist group overran much of Iraq in 2014. The PMF is officially under the command of the Iraqi army, but in practice, the militias operate independently.

In a statement Tuesday, Sudani condemned both the militia attack in Erbil and the US response.

Attacks on “foreign diplomatic mission headquarters and sites hosting military advisers from friendly nations… infringe upon Iraq’s sovereignty and are deemed unacceptable under any circumstances,” the statement said.

However, it added that the retaliatory strikes by the US on “Iraqi military sites” — referring to the militia — “constitute a clear hostile act.” Sudani said some of those injured in the strikes were civilians.