The U.S. military conducted retaliatory airstrikes in eastern Syria on Thursday against Iranian-backed groups after a deadly drone strike targeting a U.S. base in the region killed a U.S. contractor and injured six others, including five U.S. military service members, the Pentagon said.

"Earlier today, a U.S. contractor was killed and five U.S. service members and one additional U.S. contractor were wounded after a one-way unmanned aerial vehicle struck a maintenance facility on a Coalition base near Hasakah in northeast Syria at approximately 1:38 p.m. local time," the Pentagon said in a statement.

Two of the wounded service members were treated on site, while the other four Americans were medically evacuated to Coalition medical facilities in Iraq, officials said.

U.S. intelligence assessed that the one-way attack drone that struck the base was Iranian in origin, according to the statement.

"At the direction of President [Joe] Biden, I authorized U.S. Central Command forces to conduct precision airstrikes tonight in eastern Syria against facilities used by groups affiliated with Iran's Islamic Revolutionary Guards Corps (IRGC)," Defense Secretary Lloyd J. Austin III said in a statement issued late Thursday.

"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 U.S. has about 900 troops in eastern Syria providing assistance to Syrian Kurdish forces in preventing a resurgence of the Islamic State.

In recent months, some of the bases have been the target of drone attacks that had, in most instances, not led to injuries or physical damage. Iranian-backed groups in Syria are believed to have been responsible for these attacks.

"These precision strikes are intended to protect and defend U.S. personnel. The United States took proportionate and deliberate action intended to limit the risk of escalation and minimize casualties," the Pentagon statement read.

"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."

"Our thoughts are with the family and colleagues of the contractor who was killed and with those who were wounded in the attack earlier today," the defense secretary added.