The US conducted an airstrike in Syria against what it said were Iranian-affiliated facilities after a suspected Iranian drone on Thursday struck a facility housing US personnel in the country, killing an American contractor and wounding five US service members.

The contractor was an American citizen, a spokesman for US Central Command confirmed, and an additional US contractor was also wounded in the strike. “The intelligence community assess the UAV (unmanned aerial vehicle) to be of Iranian origin,” the Pentagon said.

In response to the strike, President Joe Biden authorized a precision airstrike “in eastern Syria against facilities used by groups affiliated with Iran’s Islamic Revolutionary Guards Corps (IRGC),” Secretary of Defense Lloyd Austin said in the statement.

The US, according to the Pentagon statement, “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.”

The strikes are likely to increase tensions with Iran. The US has already sanctioned Tehran for providing attack drones to Russia to use in the war in Ukraine. And on Thursday, Chairman of the Joint Chiefs of Staff Gen. Mark Milley reiterated US concerns that Iran has the potential to produce enough fissile material for a nuclear weapon in less than two weeks and manufacture one within months.

The drone intentionally crashed into its target, an official familiar with the matter told CNN. The infrastructure that was targeted in the US response was not directly related to the suspected Iranian drone itself, the official said, but was instead targeted by the US because it was known to be supporting Iranian proxy groups in the country with munitions and intelligence.

The number of casualties from the US airstrike is still being determined, the official said. The commander of US Central Command, Gen. Erik Kurilla, said the US could carry out additional strikes if there were more attacks. “We are postured for scalable options in the face of any additional Iranian attacks,” Kurilla said in a statement Thursday evening.