The rockets struck two support buildings at the Green Village base in Deir Ezzor province run by allied Kurdish-led Syrian Democratic Forces, where the US and coalition partners maintain a mission against the remnants of the Islamic State.

"At this time, four US servicemembers are being evaluated for minor injuries and possible traumatic brain injuries," the Central Command said in a statement.

The command, which oversees US operations across the Middle East, did not attribute the source of the shelling but said it was under investigation.

in January the base was also shelled in an attack blamed on Iran-backed groups, with no casualties reported.

US forces then replied by shelling the alleged source of the attack.