Three US service members were killed and dozens wounded during an unmanned aerial drone attack on US forces stationed in northeastern Jordan near the Syrian border, President Joe Biden and U.S. officials said on Sunday.

Biden blamed Iran-backed groups for the attack.

“While we are still gathering the facts of this attack, we know it was carried out by radical Iran-backed militant groups operating in Syria and Iraq,” Biden said in a statement.

At least 34 personnel were being evaluated for possible traumatic brain injury, a US official told Reuters.

“While we’re still gathering facts, this is most assuredly the work of an Iranian-backed militia group,” a second official said.

The deaths marked the first fatalities of US troops in the region since war began in Gaza. Biden said the attack occurred on Saturday night.

The attack is a major escalation of the already tense situation in the Middle East, where war broke out in Gaza after Hamas’ attack on Israel on October 7 which killed 1,200.

Israel’s subsequent assault on Gaza has killed over 26,000 Palestinians, according to the local health ministry.

While the United States has thus far maintained an official line that Washington is not at war in the region, it has made strikes against targets of Yemen’s Houthi groups that have been attacking commercial vessels in the Red Sea.

“We will carry on their commitment to fight terrorism. And have no doubt - we will hold all those responsible to account at a time and in a manner of our choosing,” Biden said in his statement released by the White House.