The United States believes its latest airstrikes on Sunday against Iran-linked militia in Syria killed up to seven people, a US official said on Tuesday, speaking on condition of anonymity to disclose the US assessment.

The deaths would be the first since the United States started carrying out retaliatory strikes 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.

US and coalition troops have been attacked at least 40 times in Iraq and Syria since early October. Statements, purportedly from the militant groups responsible, have said the assaults are in response to US support for Israel in the war in Gaza.

The US official, who spoke on condition of anonymity, said the people were killed during one of the US 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 US military assesses that no women or children were killed in the strikes, the official said.

US 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 don’t stop.

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 ISIS, which in 2014 seized large swathes of both countries but was later defeated.

There is growing concern that the Israel-Hamas conflict could spread through the Middle East and turn US troops at bases throughout the region into 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 US 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 US military patrols, restricting access to base facilities and boosting intelligence collection, including through drone and other surveillance operations, officials say.