Police fired stun grenades and tear gas at protesters who were burning tyres and hurling rocks on the strategic Al-Jumhuriyah bridge across the Tigris River leading to the highly-fortified Green Zone, an AFP photographer reported.

The bridge, barricaded by towering concrete walls, separates the Green Zone from Tahrir Square, the epicentre of the old and new demonstrations.

The highly-secure Green Zone, where government offices, parliament and the US embassy are located, is off-limits to ordinary Iraqi citizens.

In a repeat of last year's demonstrations, rallies were also held in Shiite Muslim-dominated southern towns and cities.

Overnight in the shrine city of Karbala, which was a hub of demonstrations last year, protesters skirmished with riot police who eventually fired live bullets into the air to disperse them.

In Diwaniyah, young demonstrators set car tyes on fire while in Nasiriyah, also in the south, as night fell Sunday protesters in the main square sung the national anthem amid celebratory fireworks.

Thousands of Iraqis took to the streets nationwide on Sunday to mark the first anniversary of the 2019 revolt dubbed the "October Revolution", which demanded the ouster of the entire ruling class, accused of ineptitude and corruption.

About 600 protesters were killed and 30,000 wounded in protest-related violence nationwide before demonstrations eased off and then ended with the coronavirus pandemic.

Prime Minister Mustafa al-Kadhemi, who has been in power for six months, has urged security forces to show restraint when confronting protesters.