Iraqi security forces cleared anti-government protesters from streets and squares in Baghdad and the south on Saturday, stoking fears among demonstrators that their long-running reform campaign may be suppressed.

It came a day after populist cleric Moqtada Sadr announced he would no longer back the youth-dominated movement, after he held his own mass rally that saw thousands pack the capital's streets to demand US troops leave Iraq.

By Friday morning, security forces were using tear gas and live rounds to clear protest camps across the capital, leaving at least 19 protesters wounded, medics said.

An AFP reporter saw baton-charging security personnel chase away a group of young protesters.

A medic nearby told AFP she saw riot police set fire to large tents used as field clinics to treat wounded demonstrators.

The city's military command announced it had retaken control of Ahrar Bridge, a flashpoint for clashes between security forces and demonstrators for months.

It also pushed protesters out of Tayaran Square and Mohammad Qasim highway, where new sit-ins this week were intended to pressure authorities into enacting long-awaited reforms.

By early Friday afternoon, there were hit-and-run clashes in central Baghdad but security forces had not yet entered the main protests camp in Tahrir Square.

Young men had deployed around the square carrying black shields made out of metal drums, on which they had painted the words "Tahrir Shield Squad."

- Sadr supporters pull out -
An AFP photographer saw protesters in the camp dismantling wooden stalls and colourful tents they had set up months ago.

Many of them hailed from Sadr's eponymous stronghold of Sadr City in east Baghdad and had earned a reputation as the most well-organised protesters.

One protester accused Sadr of paving the way for a wider crackdown by withdrawing political cover.

"When your people started leaving, the riot police came at 3:00 am and took the whole (Ahrar) Bridge. Why?" he asked angrily.

Sadr, a militiaman-turned-politician, is notorious for switching political positions with dizzying speed.

He backed the protests when they erupted in October and called on the government to resign -- even though he controls parliament's largest bloc and other top posts.

But last week, he called for a separate rally to demand 5,200 US troops leave Iraq, after a US strike on Baghdad killed top Iraqi and Iranian commanders earlier this month.

Thousands streamed into Baghdad for Friday's rally and. while Sadr did not attend, he hailed the turnout and said he would no longer be involved in the anti-government campaign.

The about-face prompted reports of protest camps being dismantled across the country.

In Hilla, Diwaniyah, Kut, Amarah and the Shiite shrine city of Najaf, tents were stripped down to their metal frames.

Overnight, security forces stormed a protest camp in the southern port city of Basra and forcibly dispersed activists, an AFP correspondent reported.

Their tents were burned down and municipal staff were seen clearing the charred remains on Friday to reopen the square.

- US reveals wounded troops -
The protesters have been calling for snap polls under a new electoral law, an independent prime minister and accountability for corrupt officials and those who ordered violence against demonstrators.

More than 470 people have been killed in protest-related violence since October, according to an AFP tally.

The protest movement took a serious hit in recent weeks as US-Iran tensions skyrocketed, threatening to overwhelm Iraq and eclipse their campaign for sweeping reform.

A US strike outside the Baghdad airport on January 3 killed Iranian general Qasem Soleimani and a top Iraqi commander, infuriating Iraqi officials.

Parliament slammed the strike as a a violation of Iraq's sovereignty and passed a non-binding resolution demanding that all foreign forces, including 5,200 US troops helping fight the Islamic State group, should leave.

Iran retaliated by launching a wave of missiles at US troops stationed in Iraq.

No Iraqi or US forces were killed but on Friday, the Pentagon revealed 34 American soldiers had suffered traumatic head injuries or concussion.

It was an unprecedented attack on US troops in Iraq, who had faced a wave of smaller, proxy attack in recent months that killed one US contractor and one Iraqi soldier.