BAGHDAD, Iraq－Iraqi Prime Minister Adel Abdul Mahdi on Monday condemned US airstrikes on bases of an Iraqi militia group, a move that could plunge Iraq further into the heart of tensions between the United States and Iran in the Middle East.

The US military carried out airstrikes 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.

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," Abdul Mahdi's office said.

The airstrikes will force Iraq to reconsider working with the US-led international coalition against the Islamic State terror group, the Iraqi National Security Council said in a statement.

The Kataib Hezbollah said they will hold a mass funeral ceremony on Tuesday in Baghdad near the high-security Green Zone, where the US embassy is located.

The Iraqi Foreign Ministry announced on Monday that it will summon the US ambassador in Baghdad over US attacks.

The Syrian Foreign Ministry also condemned the US airstrikes, calling them "bloody".

Meanwhile, Washington accused Iraqi authorities of having failed to "protect" US interests.

"We have warned the Iraqi government many times, and we've shared information with them to try to work with them to carry out their responsibility to protect us," a senior US State Department official told reporters in Washington on Monday.

He said the US military and diplomats are in the country "upon the invitation of the Iraqi government".

"So it's their responsibility and duty to protect us. And they have not taken the appropriate steps to do so," he said, speaking on condition of anonymity.

Iran denies role

US Secretary of State Mike Pompeo has blamed Iranian-backed forces－which helped Baghdad turn the tables on IS terrorists and are integrated into the Iraqi security apparatus－for attacks on US bases in Iraq.

Iran on Monday strongly denied any role in recent deadly attacks on the US forces in Iraq. Iranian government spokesman Ali Rabiee said: "This unsubstantiated US claim cannot justify the bombing and killing of people in violation of international regulations."

Rabiee said that the US attack was more proof of its "destructive" role in the Middle East, particularly in Iraq, and it once again showed that "as long as the US keeps its uncalled-for presence in Iraq and Syria, peace will be unattainable for all".

Tensions have risen between Teheran and Washington－Iraq's two main allies－since May 2018 when US President Donald Trump pulled out of the world powers' 2015 nuclear deal with Teheran and reimposed sanctions on the Islamic Republic.

On Tuesday, dozens of angry Iraqis broke into the US embassy compound in Baghdad after smashing a main door and setting fire to a reception area, prompting tear gas and sounds of gunfire.

Demonstrators also torched US flags in the Shiite-dominated southern cities of Basra and Najaf, and in Kirkuk north of Baghdad.

Separately, dozens of Iraqi lawmakers called on the government to review an agreement allowing the deployment of 5,200 US soldiers in the country, saying the strikes amount to a violation that renders the pact obsolete.

US Assistant Secretary of State David Schenker said the strikes were a "proportionate" response for the death on Friday of the US civilian contractor in a rocket attack.

"We don't want an escalation here, we want a de-escalation," he added.