The U.S. military on Tuesday struck targets in Iraq, Secretary of Defense Lloyd J. Austin said in a statement, in retaliation for attacks Iranian-backed militias have been launching against U.S. forces in Iraq and Syria — including one Saturday in Iraq involving missiles that the Pentagon said was one of the "larger-scale" attacks yet on a U.S. base. 

"Today, at President Biden's direction, U.S. military forces conducted necessary and proportionate strikes on three facilities used by the Iranian-backed Kataib Hezbollah militia group and other Iran-affiliated groups in Iraq," Austin's statement said. "These precision strikes are in direct response to a series of escalatory attacks against U.S. and coalition personnel in Iraq and Syria by Iranian-sponsored militias."

The strikes "targeted KH headquarters, storage, and training locations for rocket, missile, and one-way attack UAV capabilities," U.S. Central Command said in a statement Tuesday.

The "larger-scale" attack on U.S. forces Saturday that triggered the latest retaliatory strikes in western Iraq occurred against Al Asad air base. Multiple ballistic missiles and rockets were used in the attack, according to the Pentagon."It was a larger-scale attack than we have seen before," Sabrina Singh, deputy Pentagon press secretary, said Monday. 

Most of the projectiles were intercepted by air defenses, but a few got through and "there was some structural damage to noncritical facilities," Singh said. 

Four service members were evaluated for traumatic brain injuries but have since returned to duty, and one Iraqi soldier was wounded, the Pentagon said in a briefing on Tuesday. 

There have been at least 151 attacks on service members in Iraq and Syria since Oct. 17, according to the Defense Department. The U.S. military has responded a handful of times, initially with strikes on ammunition warehouses. Earlier this month, in Baghdad, the U.S. killed the leader of one of the groups who the Pentagon blamed for orchestrating the continuous attacks. 

These attacks began soon after the war between Hamas and Israel broke out in October. Though the Pentagon continues to say Israel's war is confined to Gaza and has not spread into a wider conflict, the attacks against U.S. forces in Iraq and Syria, as well as the Houthi attacks on commercial shipping, began around the same time and have added to tensions in the region. 

"The President and I will not hesitate to take necessary action to defend them and our interests. We do not seek to escalate conflict in the region," Austin's statement said. "We are fully prepared to take further measures to protect our people and our facilities. We call on these groups and their Iranian sponsors to immediately cease these attacks."

The strikes are the Pentagon's third set of military operations in just three days in three different countries – one against the terrorist group Al Shabab in Somalia on Sunday, strikes in concert with the U.K. against the Houthis in Yemen on Monday, and now, Tuesday's strike against Iranian-backed groups in Iraq.

In:
• Pentagon
• War
• Iraq
• Iran
• United States Department of Defense

Eleanor Watson

Eleanor Watson is a CBS News reporter covering the Pentagon.

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