The U.S. launched airstrikes Thursday in Iraq, 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.

Officials said multiple strikes by U.S. manned aircraft hit five locations and mainly targeted Kataib Hezbollah weapons facilities inside Iraq. The officials spoke on condition of anonymity because details about the operations were not yet public.

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. They came just hours after top U.S. defense leaders threatened retaliation for the Wednesday rocket attack, making clear that they knew who did it and that the attackers would be held accountable.