"Multiple ballistic missiles and rockets were launched by Iranian-backed militants in western Iraq targeting al-Assad Airbase," CENTCOM said in a social media post, which placed the time of the attack at 6:30 pm Baghdad time (1530GMT) Saturday evening.

Most of the projectiles were intercepted by the base's air defense systems but "others impacted on the base," the statement said.

"A number of US personnel are undergoing evaluation for traumatic brain injuries. At least one Iraqi service member was wounded," it added.

Since mid-October, there have been dozens of attacks on US and coalition forces in Iraq and Syria, deployed there to fight jihadists of the Islamic State group.

Most have been claimed by "Islamic Resistance in Iraq," a loose alliance of Iran-linked armed groups that oppose US support for Israel in the Gaza conflict.

The group said in a press release Saturday that it had carried out the latest attack.

The use of ballistic missiles marks an escalation in the attacks on US forces in Iraq and Syria, who had previously been targeted with lower-tech rockets and drones.

Saturday's air base attack comes amid soaring tensions in the Middle East following the outbreak of the Israel-Hamas war on October 7.

Five members of Iran's Islamic Revolutionary Guard Corps were also killed in a strike Saturday in Damascus that Tehran blamed on Israel, threatening reprisals.

Last Monday evening, Iran itself launched a deadly strike in northern Iraq's autonomous Kurdistan region, saying it had targeted a site used by "spies of the Zionist regime (Mossad)."

Washington has on several occasions launched strikes of its own, which it has said were to impede further assaults or to prevent imminent attacks.

According to the Pentagon, dozens of US personnel have been lightly wounded in previous attacks since late October.

There are roughly 2,500 American troops in Iraq and some 900 in Syria.