One protester was killed in the southern hotspot of Nasiriyah, with demonstrators defying gunshots and tear gas fired by riot police seeking to shut protest camps.

Activists have long worried that their months-long movement demanding a complete overhaul of Iraq's political establishment could be snuffed out.

Stoking those concerns, firebrand cleric Moqtada Sadr dropped his support for the protest movement on Friday, after holding an anti-US rally attended by thousands in Baghdad.

On Sunday, two days after Sadr supporters demanded the departure of some 5,200 American troops from Iraq, a volley of rockets landed near the US embassy in Baghad's Green Zone, two security sources told AFP.

There was no immediate claim of responsibility for the attack, the latest this month to target the high-security zone, which is also home to the Iraqi parliament.

The rocket fire came as thousands of students rallied across the country on Sunday, waving Iraqi flags and holding up two fingers in a victory sign in defiance of security forces who fired live rounds in a bid to clear them.

"Only for you, Iraq!" read a sign held by a young protester in the shrine city of Karbala, hinting at the movement's insistence on not being affiliated with any political party or outside backer.

Violence has resurged in Baghdad Iraq's Shiite-majority south this week, with more than 15 people killed as anti-government activists stepped up road closures and sit-ins.

- Protesters defiant -

On Saturday, four demonstrators were shot dead as riot police stormed protest camps across the country, according to medics, stoking fears of a broader crackdown.

In Basra, hundreds of students gathered to condemn the riot police's dismantling of their main protest camp the previous day, according to an AFP correspondent.

In Baghdad, university students marched from a campus in the city centre to the main rally area of Tahrir Square.

Riot police fired live rounds and tear gas at clusters of young protesters in the nearby Khallani and Wathba squares, but protesters threw rocks and Molotov cocktails to keep them back.

At least 17 protesters were wounded, a police source said.

Security forces have stopped short of entering Tahrir Square, where some protesters stood their ground even after many tents were dismantled.

In the southern city of Nasiriyah, security forces Sunday also fired live rounds to disperse protesters who were angered by authorities pushing them out of roads around their main protest camp in Habbubi Square.

One protester died after being shot by security forces and dozens more were impacted by tear gas in the brief skirmishes, a medical source told AFP.

At least 75 protesters suffered bullet wounds and around 100 were impacted by tear gas in brief skirmishes, a medical source told AFP.

The youth-led protests erupted on October 1 in outrage over lack of jobs, poor services and rampant corruption before spiralling into calls for a government overhaul after they were met with violence.

Protesters are now specifically demanding snap elections, the appointment of an independent premier and the prosecution of anyone implicated in corruption or recent bloodshed.

Their voices have been heard by top UN envoy in Iraq Jeanine Hennis-Plasschaert who has said: "Unaccountability and indecisiveness are unworthy of Iraqi hopes, courageously expressed for four months now."

"While death and injury tolls continue to rise, steps taken so far will remain hollow if not completed," she said Saturday.

More than 470 people have died, a vast majority of them demonstrators, in protest-related violence since the rallies erupted on October 1.

- Sadr drops support -

The defiant demonstrations on Sunday came despite Sadr's withdrawal of support for the anti-government movement.

The notoriously fickle militia leader-turned-politician initially backed the protests and called for the government's resignation although he controls the largest bloc in parliament and top ministerial posts.

On Friday, thousands attended a rally he organised in Baghdad demanding the departure of some 5,200 US troops based in Iraq.

After the mass gathering Sadr said he no longer wanted to be involved in the youth-led protest movement.

Analysts said Sadr was striving to both maintain his street credibility and win favour with Iraq's powerful neighbour Iran.

Iran holds tremendous political and military sway in Iraq and will likely have a major say in who will replace Prime Minister Adel Abdel Mahdi who submitted his resignation in December.

Meanwhile anger at the United States has swelled since an American drone attack near Baghdad airport on January 3 killed top Iranian general Qasem Soleimani and leading Iraqi military official Abu Mahdi al-Muhandis.

On Sunday a volley of rockets hit near the US embassy in Baghdad's Green Zone without causing casualties, security sources said.

One source said three Katyusha rockets were fired while the Iraqi security forces said five rockets struck the Green Zone.