The US struck Iran-aligned militias in Iraq on Monday, officials said. The strikes came after an attack by militants wounded three US military personnel at a base in Erbil in the northern Kurdistan region.
The Iranian-backed militia Kataib Hezbollah and affiliated groups claimed responsibility for the attack.
Iran-aligned groups oppose Israel's offensive in the Hamas-run Gaza Strip. The US is Israel's most critical ally.
The US military has come under attack at least 100 times in Iraq and Syria since the start of the war between Israel and Hamas.
The US base in Erbil has been targeted many times previously, including with a drone attack on October 26, which penetrated air defenses but did not detonate. In December, the US embassy compound came under mortar fire.
What did US officials say about the strikes?
National Security Council spokeswoman Adrienne Watson said one of the wounded US soldiers suffered critical injuries.
"[US President Joe Biden] 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 US military said that the strikes likely killed "a number of Kataib Hezbollah militants" and destroyed multiple facilities.
"US military forces conducted necessary and proportionate strikes on three facilities used by Kataeb Hezbollah and affiliated groups in Iraq," US Defense Secretary Lloyd Austin said.
"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. We will always protect our forces," Michael Erik Kurilla, head of the US Central Command, said in a statement.
Earlier, on Monday, an Israeli airstrike on a Damascus, Syria, neighborhood killed a high-ranking Iranian general, local media reported. Iran-backed militant groups in the region had said they would take revenge for the killing.