The U.S. military conducted several airstrikes in Syria on Thursday against Iran-aligned groups hours after an Iranian drone attack killed a U.S. contractor and injured five service members, the Pentagon said. 

President Biden directed the U.S. military to carry out retaliatory strikes against facilities affiliated with Iran’s Revolutionary Guard after the Iranian attack on a coalition base housing American personnel near Hasakah on Thursday night, Secretary of Defense Lloyd Austin said.

“The airstrikes were conducted in response to today’s attack as well as a series of recent attacks against Coalition forces in Syria by groups affiliated with the IRGC,” he added. 

The Pentagon said the U.S. “took proportionate and deliberate action intended to limit the risk of escalation and minimize casualties.”

“As President Biden has made clear, we will take all necessary measures to defend our people and will always respond at a time and place of our choosing,” Austin said. “No group will strike our troops with impunity.”

Three service members and a second U.S. contractor were evacuated to coalition medical facilities in Iraq, while two others were treated on site.

The U.S. strikes killed at least eight pro-Iranian fighters, according to the U.K.-based Syrian Observatory for Human Rights, which monitors the war in Syria.

Iranian-backed groups have attacked U.S. groups 78 times since the start of 2021, according to Army General Erik Kurilla, the head of Central Command.

“We are postured for scalable options in the face of any additional Iranian attacks,” Kurilla said in a statement Thursday.

The U.S. maintains roughly 900 service members in Syria to conduct counterterrorism operations.