Four U.S. service members were injured early Thursday morning when their base in northeast Syria came under rocket fire, the U.S.-led anti-ISIS coalition said in a statement.
The troops were being evaluated for "minor injuries and possible traumatic brain injuries," according to the statement Thursday from Operation Inherent Resolve.
The attack happened at 1:09 a.m. local time at a base known as Green Village, just east of the Euphrates River and near major oil fields. Two rounds of indirect fire hit two support buildings at the base, according to the statement.
The brief statement provided no additional details of the attack, with the coalition saying the incident is under investigation.
The Syrian Observatory for Human Rights, a U.K.-based organization that monitors the war in Syria, said local sources reported rockets being launched from an area just west of the Euphrates known to be held by Iranian-backed militias. While five rockets reached the base, only two exploded, according to the monitor.
U.S. forces have been in Syria since 2015 helping local forces fight the ISIS terrorist group. Roughly 900 U.S. troops remain in Syria, despite former President Donald Trump's repeated attempts to withdraw them.
U.S. officials have blamed Iranian proxy militias for previous attacks on American troops in the same area as Thursday's attack.
U.S. forces at Green Village came under indirect fire in January that Operation Inherent Resolve commander Maj. Gen. John Brennan Jr. blamed on Iranian-backed militias. No U.S. troops were injured in that attack, but American forces responded with artillery strikes.
In June, U.S. forces at the nearby al Omar oil field also came under rocket fire in what was perceived as retaliation for U.S. airstrikes the day before on facilities on the Iraq-Syria border used by Iranian-backed militias. U.S. troops were not injured in the June attack, but fired back in self-defense.
For years, the United States and Iran have engaged in tit for tat in Iraq and Syria, most dramatically coming to the brink of war in 2020 when a U.S. drone strike killed Iranian Gen. Qasem Soleimani and Iran responded with a missile strike on an Iraqi base housing U.S. troops, giving traumatic brain injuries to more than 100 service members.