The U.S. launched airstrikes in Iraq Thursday, American officials said, targeting the Iranian-backed Shia militia members believed responsible for the rocket attack that killed and wounded American and British troops at a base north of Baghdad.

One U.S. official said multiple strikes targeted Kataib Hezbollah weapons facilities inside Iraq. The strikes were joint operation with the British, that official said. The officials spoke on condition of anonymity because operations were still going on.

The strikes marked a rapid escalation in tensions with Tehran and its proxy groups in Iraq, just two months after Iran carried out a massive ballistic missile attack against American troops at a base in Iraq.