The United States on Friday carried out a series of military strikes against Iran-backed militants in half a dozen sites in Iraq and Syria, according to a U.S. Defense Department official, marking a sharp escalation of the war in the Middle East that the Biden administration has for four months sought to avoid.

President Biden had promised to respond to a drone attack in Jordan on Sunday that killed three American soldiers and injured at least 40 more service members. The military action sought to send a message to Iran and the militias it backs that continued attacks on U.S. troops in the region and international ships in the Red Sea will draw a response.