In a statement, US Defense Secretary Lloyd Austin said the strikes targeted a training facility near the city of Albu Kamal and a safe house near the city of Mayadeen. He said President Joe Biden ordered the strikes.
"The President has no higher priority than the safety of US personnel, and he directed today's action to make clear that the United States will defend itself, its personnel, and its interests," Austin said in a statement.
Local sources also said the strikes targeted a camp run by pro-Iranian militias in an area west of Albu Kamal, in Deir al Zor province. The other strike was near a bridge close to the city of Mayadeen, near the Iraqi border and stronghold of pro-Iranian militias, the sources said.
The strike is the third since October 26 as the United States attempts to quell wave after wave of drone and rocket attacks against American troops in Syria and Iraq, triggered by the Israel-Hamas war.
Iran and its supporters say the United States shares responsibility for Israel's declared war against Palestinian militant group Hamas, which is also backed by Iran.
US and coalition troops have been attacked at least 40 times in Iraq and Syria by Iran-backed forces in recent weeks. At least 45 US troops have suffered traumatic brain injuries or minor wounds
The United States has 900 troops in Syria, and 2,500 more in neighboring Iraq, on a mission 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.
A US official, speaking on condition of anonymity, said the strikes took place within the past several of hours and added that a US review was underway to determine whether the they killed or wounded anyone.
There is growing concern that the Israel-Hamas conflict could spread through the Middle East and turn US troops at isolated bases into targets.
The United States has sent warships and fighter aircraft to the region since the Israel-Hamas conflict erupted on October 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.
