U.S. military forces on Monday carried out precision strikes against Iranian-backed militia groups in Iraq, including Kataib Hezbollah, Defense Secretary Lloyd Austin said in a statement. The strikes followed a drone attack by the groups on Irbil air base earlier in the day that injured three service members. One is in critical condition, he said.

U.S. strikes targeted three locations used by Kataib Hezbollah and affiliated groups for aerial drone activities, National Security Council spokeswoman Adrienne Watson said in a statement.

President Biden was immediately briefed on the attack on U.S. personnel, Watson said, adding that he directed the retaliatory strikes.

Iranian-backed militia groups are believed to have waged a spate of attacks on U.S. and coalition troops in Iraq and Syria, as anger in the Middle East grows over U.S. support for Israel’s military campaign in Gaza. More than 20,000 people have been killed in Gaza since the war began. The Washington Post last month reported that since Oct. 17, U.S. troops in Iraq and Syria had faced near-daily assaults from rocket fire and one-way drones.

A senior Kataib Hezbollah official, who spoke on the condition of anonymity due to the sensitivity of the matter, said the group’s operations against U.S. forces in Iraq are partly because of the United States’ support for Israel in its war with Hamas, and also because it considers the U.S. presence in Iraq an “occupation.”

“Our operations will continue until the departure of the last American soldier,” the official said.

The Biden administration has carried out similar retaliatory strikes in Syria, including on an Iranian weapons facility and on sites associated with Iran’s Islamic Revolutionary Guard Corps in October and November.

The administration is aware that any overreaction to the attacks on U.S. personnel could inflame a broader regional war. “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 the statement Monday.

About 3,500 U.S. troops remain in Iraq and Syria to prevent a resurgence of the Islamic State extremist group. Iran has long backed militias in an effort to dislodge U.S. presence in the region.

“These strikes are intended to hold accountable those elements directly responsible for attacks on coalition forces in Iraq and Syria and degrade their ability to continue attacks,” Gen. Michael Erik Kurilla, head of U.S. Central Command, said in a statement Monday night.

According to the statement by Centcom, early assessments indicate that the airstrikes Monday probably killed a “number of Kataib Hezbollah militants.” The Shiite militant group was designated a foreign terrorist organization by the State Department in 2009.

In a statement Tuesday, Iraqi Prime Minister Mohammed Shia al-Sudani condemned the drone attack and the U.S. response, which he said killed one Iraqi service member and injured 18 others, including civilians.

“This constitutes a clear hostile act. It runs counter to the pursuit of enduring mutual interests in establishing security and stability, and it opposes the declared intention of the American side to enhance relations with Iraq,” he said.

The earlier Centcom statement said there were “no indications that any civilian lives were affected.”