Two anti-government protesters were killed in clashes with security forces in the Iraqi capital on Friday, hours after thousands of supporters of Shiite cleric Moqtada Sadr rallied separately to demand the ouster of US troops.

Four NGO workers, three of them French nationals, were also reported missing in Baghdad, rocked since October by a youth-dominated protest movement demanding a government overhaul, early elections and more accountability.

More than 470 people have died in protest-related violence since October, most of them demonstrators, and violence has spiked this week.

Young anti-government demonstrators shut down streets in Baghdad and across the south this week with burning tyres and metal barricades Young anti-government demonstrators shut down streets in Baghdad and across the south this week with burning tyres and metal barricades Photo: AFP / -

On Friday, one protester was struck in the neck by a live round while another died after being hit with a military-grade tear gas canister in clashes with security forces, medical and police sources told AFP.

It marked a sudden and bloody turn as thousands of men, women and children had gathered in Baghdad earlier the same day without incident to demand US troops withdraw.

A vowed enemy of US troops, Sadr had called for "a million-strong" rally but did not attend himself.

"Get out, get out, occupier!" they chanted.

Supporters of Sadr rallied near his residence in the central holy shrine city of Najaf in early December last year Supporters of Sadr rallied near his residence in the central holy shrine city of Najaf in early December last year Photo: AFP / Haidar HAMDANI

One protester carried a cardboard cut-out of Donald Trump on the gallows, another of the US president banging himself on the head with a shoe.

A statement read by his representative at the rally demanded all foreign forces leave Iraq, Iraqi-American security agreements be cancelled, Iraqi airspace be closed to US military aircraft and for Trump not to act "arrogant" when addressing Iraqi officials.

"If all this is implemented, we will deal with it as a non-occupying country -- otherwise it will be considered a country hostile to Iraq," the statement read.

Sadr, long opposed to US troops being in Iraq, called for 'a million-strong, peaceful, unified demonstration to condemn the American presence and its violations' Sadr, long opposed to US troops being in Iraq, called for 'a million-strong, peaceful, unified demonstration to condemn the American presence and its violations' Photo: AFP / -

America's military presence has been a hot-button issue in Iraq since a US drone strike killed Iranian general Qasem Soleimani and a top Iraqi commander in Baghdad on January 3.

Outraged parliamentarians swiftly voted all foreign forces, including 5,200 US troops helping fight the Islamic State group, should leave.

US-led operations against the Islamic Strate group have been on hold after Iran carried out retaliatory missile strikes against Iraqi bases housing coalition troops US-led operations against the Islamic Strate group have been on hold after Iran carried out retaliatory missile strikes against Iraqi bases housing coalition troops Photo: AFP / Ayman HENNA

Baghdad offered to discuss a withdrawal timeline, but the US special envoy for the anti-IS coalition, James Jeffrey, said Thursday there was no "real engagement".

In response to Soleimani's killing, Iran fired ballistic missiles on an Iraqi airbase where US troops are stationed, prompting fears of a regional war.

The US said it had received prior warning of the strikes on Ain al-Asad, allowing troops to take cover.

No Iraqi or US forces were killed and Trump had insisted no one was wounded either, but the Pentagon on Friday said 34 American soldiers had suffered traumatic head injuries or concussions.

Iraqi protesters carry away the body of a comrade hit by a tear gas canister during clashes with riot police in eastern Baghdad Iraqi protesters carry away the body of a comrade hit by a tear gas canister during clashes with riot police in eastern Baghdad Photo: AFP / Ahmad AL-RUBAYE

Tehran seized on the US strike to insist American troops leave the region, and its Supreme National Security Council issued a statement backing Sadr's rally on Friday.

Pro-Tehran groups in Iraq's Hashed al-Shaabi military force also endorsed the protest.

"To Trump, the fool -- the people's message of rejection was clear: if you don't leave voluntarily, you'll be ousted despite yourself," Hashed commander Qais al-Khazali tweeted.

There had been worries Sadr supporters might storm the high-security Green Zone, home to the US embassy and other foreign missions, or the main anti-government protest camp in the capital's Tahrir Square.

But they did not head for either, and instead several thousand youth flocked to Tahrir to insist on domestic reform.

Some had feared that with all the attention on Sadr's rally, security forces would try to clear their camp.

"The return of protesters to Tahrir is meant to prove ourselves, first, and to protect its peacefulness," demonstrator Karrar al-Saadi told AFP.

Baghdad has been gripped by kidnappings and shoot-outs which protesters say are meant to intimidate them.

Separately, French NGO SOS Chretiens d'Orient (Christians of the Middle East) said three French and one Iraqi worker went missing on Monday in Baghdad, where the foreigners were renewing their Iraqi visas.

No group has claimed responsibility and no ransom demand has been received, the organisation's director Benjamin Blanchard told reporters in Paris.

Sadr, 46, battled US forces with his Mehdi Army militia after the 2003 invasion of Iraq but is now a fickle politician, notorious for switching alliances.

He backed anti-regime protests early on, but also controls parliament's largest bloc and top ministerial posts.

On Friday evening, Sadr tweeted to hail the turnout at his rally but said he would no longer be involved in anti-regime efforts.

"From now on, I will try not to intervene in their business, neither negatively nor positively," he said.

Carnegie Middle East Center expert Harith Hasan said Sadr sought to sustain his "multiple identities" -- one as a reformist and populist, the other as a leading anti-American voice.

Playing both sides could earn Sadr favour with Iran and empower him in paralysed negotiations over the next premier, Hasan said.

But Friday's intra-Shiite alliance was not likely to last, Hasan said, predicting: "Once this protest is over, this honeymoon between Sadr and the other pro-Iran factions will eventually vanish,"