WASHINGTON — United States warplanes struck five targets in southern Iraq on Thursday night, hitting back at an Iraqi militia with ties to Iran that is believed to have been part of a rocket attack on Wednesday that killed two Americans and a British soldier, American officials said.

The airstrikes, which were supported by the British military, targeted the militia Kataib Hezbollah and facilities that were believed to store the type of rockets used in the attack on coalition forces on Wednesday. It is not known how many militia members, if any, were killed, a military official said.

“The United States will not tolerate attacks against our people, our interests or our allies,” Defense Secretary Mark T. Esper said in a statement after the strikes.

Mr. Esper’s language falls in line with a now familiar pattern as Washington moves to curb malign efforts from Iran and its proxies across the region.