The US embassy in Baghdad's heavily fortified Green Zone came under attack from rocket fire on Sunday evening.

Five rockets crashed into a riverbank near the embassy in the Iraqi capital without causing any injuries, the US Joint Operations Command said in a statement, but AFP news agency citing a security source said three of the rockets "directly hit the US embassy". One slammed into a cafeteria at dinner time, it added.

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If confirmed, the attack would mark the first time the complex had been directly hit in the third attack against the embassy this month.

Caretaker Prime Minister Adel Abdul Mahdi swiftly condemned the attack in a statement, calling it an "aggression" that could "drag Iraq into becoming a war zone".

In a statement, the United States urged Iraq to protect the embassy.

"We call on the Government of Iraq to fulfill its obligations to protect our diplomatic facilities," a State Department spokesperson said in a statement.

Wathiq al-Hashemi, an Iraqi political analyst, told Al Jazeera that the attack was an "embarrassment" for the government of Abdul Mahdi, who resigned in November under pressure from Iraq's months-long protest movement demanding an overhaul of the country's political system.

"Abdul Mahdi's position is not one to envy. He had told armed groups to stop these kinds of attacks on the US embassy, but to no avail," al-Hashemi said.

"What is interesting to note is that the pro-Iranian militias have denied any role in this attack, saying they did not target the embassy and that it could have been other armed groups. I expect there will be a US response but it remains to be seen whether it will be a military one or not."

Protesters killed

Meanwhile, one protester was killed in Baghdad and another in the southern city of Nasiriyah as security forces tried to clear sit-in protest camps, medical sources told Al Jazeera. Scores of protesters were wounded.

More than 500 demonstrators have been killed since the protest movement began in October, with rights groups accusing security forces of using excessive force.

The protesters are demanding the removal of what they consider a corrupt ruling elite and an end to foreign interference in Iraqi politics.

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Unrest resumed last week, after a lull of several weeks, following the January 3 US drone strike that killed Iranian General Qassem Soleimani and Abu Mahdi al-Muhandis, an Iraqi commander of the pro-Iranian Hashd al-Shaabi militia group.

The killing, to which Iran responded with ballistic missile attacks on two Iraqi bases hosting US troops, has revived tensions in Iraqi politics and delayed the formation of a new government.

Amid growing calls for an end to interference, the Iraqi Parliament on January 5 backed a nonbinding resolution for all foreign troops - including 5,200 US soldiers - to leave the country.

University students shout slogans during the anti-government protests in Baghdad [Thaier al-Sudani/Reuters]

Shia leader cancels march

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Meanwhile, leading Shia leader Moqtada al-Sadr had called for renewed demonstrations against the US in Baghdad and other cities on Sunday but cancelled them with his office giving "avoiding internal strife" as the reason.

On Friday, tens of thousands protested against the US military presence in Iraq in a march.

Sadr, who has millions of supporters in Baghdad and the south, said on Saturday he would end his involvement in the anti-government unrest.

Al-Sadr's supporters have bolstered the protesters and at times helped shield them from attacks by security forces and unidentified gunmen, but began withdrawing from sit-in camps on Saturday following his announcement.

The Iraqi High Commission on Human Rights called on all sides to exercise self-restraint and keep the demonstrations peaceful.

Additional reporting by Linah Alsaafin in Baghdad