"This is an important day, we are here to keep the movement going," student Mohamed Ali said in the square, epicentre of the revolt.

The renewed mobilisation has retained protesters' key demand of the ouster of the entire ruling class accused of corruption and being beholden to neighbouring Iran.

Iraq is the second largest oil exporter in the world but has struggled to pay salaries for its bloated public sector.

"We have the same demands as last year," Ali told AFP.

In a months-long revolt launched in October 2019, hundreds of thousands of demonstrators camped out in Baghdad and southern cities to demand a total overhaul of a political system failing to deliver basic services and salaries.

About 600 protesters were killed and 30,000 wounded in clashes with security forces before the movement lost momentum then ground to a halt in the spring due to the coronavirus crisis and rising US-Iran tensions.

Since Saturday, military checkpoints and roadblocks have been erected around the square and the Green Zone, which is off-limits to Iraqi citizens.

The fortified Green Zone -- site of parliament, government offices and the US embassy -- is separated by a bridge from the square.

Riot police stationed around major thoroughfares have barred demonstrators waving Iraqi flags from trying to cross.

Other parallel bridges have also been sealed off.

With no central leadership behind the protests, activists are divided over whether to stay put in Tahrir or head to the Green Zone at the risk of violence breaking out.