Iraqi Prime Minister Adel Abdul Mahdi on Monday condemned US air strikes on Iranian-backed Iraqi militia bases, a move that could plunge Iraq further into the heart of a proxy conflict between Washington and Tehran.
The United States military carried out air strikes on Sunday against the Kataib Hezbollah militia in response to the killing of a US civilian contractor in a rocket attack on an Iraqi military base, officials said.
Iraqi sources said at least 25 militia fighters were killed and 55 wounded.
"The prime minister described the American attack on the Iraqi armed forces as an unacceptable vicious assault that will have dangerous consequences," his office said.
Tensions have risen between Tehran and Washington since last year when President Donald Trump pulled out of a 2015 nuclear deal and reimposed sanctions.
Earlier this month, US Secretary of State Mike Pompeo blamed Iranian-backed forces for attacks on bases in Iraq and said any attacks by Tehran or proxies harming Americans or allies would be "answered with a decisive U.S. response."
US officials said Washington had exhibited patience amid escalating provocations from Iran and its allies, but that it was time to re-establish deterrence against aggression.
"After so many attacks it was important for the president to direct our armed forces to respond in a way that the Iranian regime will understand," US special representative for Iran Brian Hook said in a news briefing.
Iran denies involvement in attacks on US forces and has condemned the raids as "terrorism".
The strikes come at a time of protests in Iraq with thousands taking to the streets to condemn, among other things, militias such as Kataib Hezbollah and their Iranian backers.
They also demand an overhaul of a political system they see as corrupt and keeping most Iraqis in poverty. About 400 people in Basra protested against the strikes, demonstrating in support of the militias.
The air strikes brought threats of reprisal. A leading militia leader vowed revenge against US forces in Iraq.
"Our response will be very tough on the American forces in Iraq," senior commander Jamal Jaafar Ibrahimi, also known as Abu Mahdi al-Mohandes, said on Sunday.
Mohandes is a senior commander of Iraq's Popular Mobilization Forces (PMF), an umbrella grouping of paramilitary organizations mostly consisting of Iranian-backed Shiite militias that was integrated into Iraq's armed forces.
He is also one of Iran's most powerful allies in Iraq and formerly headed Kataib Hezbollah, which he founded.
Iraqi security sources said US forces in northern Iraq were ramping up security.
Iraq's government will announce its official position later on Monday, Abdul Mahdi said.
The PMF bolstered Iraq's security forces during their battle to retake a third of the country from ISIS. They were later formally integrated into Iraq's official security structure.
Iraq's Fatih alliance, a political bloc representing the militias which holds the second largest number of seats in parliament, condemned the air strikes.
Their main rival, populist cleric Moqtada al-Sadr who leads parliament's largest group, said he was willing to work with them to end US military presence in Iraq. But he also called on them to reign in their militias so as not to provide an excuse for further US attacks.
Iraq's influential top Shiite cleric Grand Ayatollah Ali al-Sistani condemned the strikes but his office also denounced attacks by Iranian-backed militias on US personnel.
He urged Iraqi authorities to prevent such attacks and "ensure Iraq does not become a field for settling regional and international scores and that others do not interfere in its internal affairs."
Abdul Mahdi said his government's policy was to keep Iraq out of regional alliances and away from war.
Any escalation risks Iraq becoming the battlefield for a proxy war between the United States and Iran, which would also ensnare regional allies of both sides.
Israeli Prime Minister Benjamin Netanyahu's office said he congratulated Pompeo "on the important operation by the United States against Iran and its proxies in the region".
Russia, which like Iran and Lebanon's Hezbollah backs Bashar Assad's regime in Syria's war, said the strikes were unacceptable and counterproductive. The Syrian regime also condemned the strikes.