The U.S. military struck targets connected with Iranian-backed militias in Iraq after a Christmas Day drone attack injured four U.S. troops on Monday.

President Joe Biden ordered the strikes on Kataib Hezbollah targets after a drone attack on Erbil Air Base in northern Iraq on Monday that left one U.S. soldier in critical condition.

The U.S. Department of Defense also said the precision strikes were in response to attacks on U.S. troops in Syria, also by Iranian-aligned militants.

“The President and I will not hesitate to take necessary action to defend the United States, our troops, and our interests,” U.S. Secretary of Defense Lloyd Austin said in a statement. “There is no higher priority. 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.”

The U.S. Central Command, which has responsibility for the Middle East and Central Asia, said in a statement that early assessments indicated the airstrikes destroyed the targeted facilities and likely killed “a number of Kataib Hezbollah militants.” The Central Command also said that it believed no civilian lives were lost and that it would continue to evaluate the results of the strikes.

“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,” said Gen. Michael Erik Kurilla, U.S. Central Command Commander. “We will always protect our forces.”