CNN
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Three US Army soldiers were killed and at least two dozen service members were injured in a drone attack overnight on a small US outpost in Jordan, US officials told CNN, marking the first time US troops have been killed by enemy fire in the Middle East since the beginning of the Gaza war.

The killing of three Americans at Tower 22 in Jordan near the border with Syria is a significant escalation of an already-precarious situation in the Middle East. Officials said the drone was fired by Iran-backed militants and appeared to come from Syria.

US Central Command confirmed in a statement on Sunday that three service members were killed and 25 injured in a one-way drone attack that “impacted at a base in northeast Jordan.”

President Joe Biden vowed on Sunday to hold those responsible for the attack “to account,” saying that while facts are still being gathered, “We know it was carried out by radical Iran-backed militant groups operating in Syria and Iraq.”

“These service members embodied the very best of our nation: Unwavering in their bravery. Unflinching in their duty. Unbending in their commitment to our country — risking their own safety for the safety of their fellow Americans, and our allies and partners with whom we stand in the fight against terrorism. …  [H]ave no doubt – we will hold all those responsible to account at a time and in a manner our choosing.”

As of Friday, there had been more than 158 attacks on US and coalition forces in Iraq and Syria, though officials have described the constant volley of drones, rockets, and missiles as unsuccessful as they have frequently not caused serious injury or damage to infrastructure.

It’s unclear why air defenses failed to intercept the drone, which appears to be the first known attack on Tower 22 since attacks on US and coalition forces began on October 17. US forces at the outpost are there as part of an advise-and-assist mission with Jordan.

US officials have repeatedly said they do not want to see the increasingly high tensions across the Middle East broaden into a regional war. Asked last week whether the Pentagon assessed that Iranian proxies were stepping up their attacks on US forces, Deputy Pentagon Press Secretary Sabrina Singh said, “Not necessarily, no.”

In a previously recorded interview with ABC News that aired Sunday morning, Chairman of the Joint Chiefs of Staff Gen. CQ Brown said part of the US’ work is to “make sure as things have happened in the Middle East is not to have the conflict broaden.”

“The goal is to deter them and we don’t want to go down a path of greater escalation that drives to a much broader conflict within the region,” he said.

There have been dozens of injuries since the attacks began — a senior military official told reporters last week there were roughly 70 — but the Pentagon has classified most of them as minor, aside from one US soldier who was critically injured in an attack in Iraq on Christmas Day.

Chief Warrant Officer 4 Garrett Illerbrunn from the 82nd Combat Aviation Brigade was set to be sent back to the US for further treatment after he critically injured in a drone attack on Erbil Airbase.

The US has taken several retaliatory actions against the Iran-backed groups in Iraq and Syria, one as recently as last week, when the US struck three facilities in Iraq used by Kataib Hezbollah and other Iran-affiliated groups.

The killing of three Americans also comes as the US and Iraq are expected to begin talks soon about the future of the US military presence in the country.

This is a developing story and will be updated.