Three U.S. soldiers were killed and dozens wounded in a drone strike by a pro-Iranian militia on a U.S. outpost in northeast Jordan overnight, President Biden said in a statement on Sunday.

Why it matters: This is the most serious attack on U.S. forces in the Middle East since Hamas launched its Oct. 7 attack and it is the first such attack in Jordan.

• The Hamas attack, and the resulting war with Israel, have marked an escalation of tension and skirmishes in the region, including Houthis targeting ships crossing the Red Sea.

Of note: CNN first reported on the attack — which Iran's foreign ministry denied on Monday, according to Iranian state media.

What they're saying: "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. … And have no doubt — we will hold all those responsible to account at a time and in a manner our choosing," Biden said.

Meanwhile, the Iranian state-run IRNA news agency reports that Tehran's foreign ministry spokesperson Nasser Kanaani said: "These claims are made with specific political goals to reverse the realities of the region."

Driving the news: U.S. Central Command said in a statement that 25 U.S. soldiers were wounded in the attack.

• The attack occurred at an outpost known as Tower 22, located near the Syrian border.
• Jonathan Lord, a senior fellow at CNAS and a former Department of Defense official, said the outpost sits at the intersection of the borders of Jordan, Iraq and Syria.
• It is key terrain in close proximity to areas the Kataib Hezbollah, a pro-Iranian militia, has seized, Lord said.

The other side: A Jordanian government spokesman claimed the attack was not on a U.S. base in Jordan, but against the al-Tanf base in Syria.

• The spokesperson later walked back the statement, acknowledging the attack took place on the Jordanian-Syrian border. He also condemned the attack and said U.S. soldiers are assisting Jordan with border protection and counterterrorism efforts.

The big picture: The Pentagon said there have been more than 150 attacks on U.S. bases and forces in Syria, Iraq and the Red Sea since Oct. 7.

• A strike on U.S. forces in Iraq on Christmas Day resulted in three injuries to service members, including one classified as critical.
• President Biden ordered retaliatory strikes on the Kataib Hezbollah, who claimed credit for that attack, on Dec. 26.

Editor's note: This story has been updated with an infographic image and comment from Jordanian government and Iranian foreign ministry spokespeople.