Baghdad slammed Washington on Wednesday after U.S. airstrikes killed at least two people in western Iraq.
Iraqi authorities accused the U.S. of contributing to a "reckless escalation" of violence in the region after the airstrikes targeted Iran-backed groups.
The pre-dawn air raid came against an already explosive regional backdrop, fueled by Israel's war on Gaza.
Pentagon chief Lloyd Austin said U.S. forces had carried out "necessary and proportionate strikes" against "three facilities used by the Iranian-backed Ketaeb Hezbollah militia group (the Hezbollah Brigades) and other Iran-affiliated groups in Iraq."
"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," he said, referring to the U.S.-led coalition against the Daesh terrorist group.
U.S.-led coalition forces in Iraq and Syria have been targeted in more than 150 attacks since mid-October, many of them claimed by the Islamic Resistance in Iraq, a loose alliance of Iran-linked groups that oppose U.S. support for Israel in the Gaza conflict.
U.S. forces have carried out a number of airstrikes against the groups they hold responsible, drawing a backlash from Iraq which has demanded the coalition's withdrawal, accusing it of overstepping its mission to assist the campaign against Daesh.
"This unacceptable act undermines years of cooperation, blatantly violates Iraq's sovereignty and contributes to a reckless escalation ... at a time when the region is already grappling with the danger of expanding conflict," said a spokesman for Iraqi Prime Minister Mohammed S. Al Sudani.
"We will treat these operations as acts of aggression and take necessary actions to preserve the lives and dignity of Iraqis," added Yehia Rasool, the Iraqi leader's spokesman for military affairs.
His comments were echoed by Iraqi National Security Adviser Qassem al-Araji who said the pre-dawn strikes were another "flagrant violation of Iraq's sovereignty" and "do not help bring calm."
"The U.S. side should pile on pressure for a halt to the (Israeli) offensive in Gaza rather than targeting and bombing the bases of an Iraqi national body," Araji said in a post on X, formerly Twitter, referring to the Hashed al-Shaabi.
According to Iraqi sources, the U.S. strikes targeted the Hezbollah Brigades, a group affiliated with the Hashed al-Shaabi (Popular Mobilisation force), an alliance of Iran-backed former paramilitary groups now integrated in Iraq's regular armed forces.
They hit sites in the Jurf al-Sakhr area, south of Baghdad, as well as in the Al-Qaim area on the border with Syria.
After previous U.S. strikes, the Iraqi prime minister has called for the U.S.-led coalition to leave, saying the deployment must end to ensure Iraq's security.
There are roughly 2,500 U.S. troops in Iraq and some 900 in neighboring Syria.
The U.S. military said the latest strikes targeted Hezbollah Brigades "headquarters, storage and training locations for rocket, missile and one-way attack UAV (drone) capabilities."
