U.S. troops in Iraq and Syria have been attacked about 150 times by Iran-aligned militants since the Israel-Gaza war started in October.

On Saturday, four U.S. personnel suffered traumatic brain injuries after Iraq's Ain al-Asad air base was hit by multiple ballistic missiles and rockets fired by Iranian-backed militants from inside Iraq.

The officials, speaking on the condition of anonymity, said the strikes were targeting multiple locations.

The attacks against the United States are seen as retaliation for its support of Israel in its war against Iran-backed Palestinian militant group Hamas.

The U.S. has 900 troops in Syria and 2,500 in Iraq, advising and assisting local forces to prevent a resurgence of Islamic State, which in 2014 seized large parts of both countries before being defeated.

(Reporting by Idrees Ali and Phil Stewart, editing by Deepa Babington)