The deaths would be the first since the U.S. started carrying out retaliatory strikes in the past month against militia who Washington blames for attacking American troops at bases in Iraq and Syria. The other strikes have hit unoccupied facilities, including for storage of weaponry.

U.S. and coalition troops have been attacked at least 55 times in Iraq and Syria since Oct. 17, injuring 59 personnel, though all have returned to duty.

Statements, purportedly from the militant groups responsible, have said the assaults are in response to U.S. support for Israel in the war in Gaza.

The U.S. official said the people were killed during one of the strikes on the training facility near the city of Al Bukamal.

A second strike that the Pentagon says was carried out at a safe house near the city of Mayadeen may have killed an additional person, the official said.

The U.S. military assesses that no women or children were killed in the strikes, the official said.

At the Pentagon, spokesperson Sabrina Singh said an assessment was ongoing.

"We are aware that there were IRGC affiliated members in the proximity of the facilities that were struck by our aircraft. But I don't have more on casualty numbers or anything else to read out," Singh told reporters, using an acronym for Iran's Revolutionary Guards.

U.S. Defense Secretary Lloyd Austin on Monday left open the possibility of more strikes against Iran-linked groups if attacks against American forces in Iraq and Syria continue.

The United States has 900 troops in Syria, and 2,500 more in neighboring Iraq, to advise and assist local forces trying to prevent a resurgence of Islamic State, which in 2014 seized large swathes of both countries but was later defeated.

There is growing concern the Israel-Hamas conflict could spread through the Middle East, with U.S. troops at bases throughout the region becoming targets.

The United States has deployed additional air defenses and sent warships and fighter aircraft to the region since the Israel-Hamas conflict erupted on Oct. 7, including two aircraft carriers, to try to deter Iran and Iran-backed groups.

The number of troops added to the region is in the thousands.

Reuters has reported that the U.S. military was taking new measures to protect its Middle East forces during the ramp-up in attacks by suspected Iran-backed groups, and was leaving open the possibility of evacuating military families if needed.

The measures include increasing U.S. military patrols, restricting access to base facilities and boosting intelligence collection, including through drone and other surveillance operations, officials say.