Tens of thousands of supporters of Shia cleric Moqtada Sadr packed the streets of the Iraqi capital Friday in a show of force as preparations ramp up for June parliamentary elections.

Despite the novel coronavirus pandemic, tens of thousands gathered shoulder-to-shoulder for noon Muslim prayers in Baghdad's Tahrir Square, spilling out into the surrounding streets.

The Sadrist movement had called for protests to back the reform of what it says is Iraq's corrupt state, but its populist leader has also been making moves ahead of next year's vote.

In a tweet this week, Sadr said he expected major wins for his party and would push for the next prime minister to be a member of the Sadrist movement for the first time.

Sadrists had already won big in the May 2018 vote with 54 of parliament's 329 seats, granting him the biggest single bloc.

This summer, Prime Minister Mustafa al-Kadhemi set June 2021 as the date for the next parliamentary elections -- nearly a year ahead of schedule to fulfil a key demand of the youth-dominated protest movement that erupted across Iraq in October 2019.

They will take place under a new electoral law agreed by parliament that will see district sizes reduced and votes for individual candidates replacing list-based ballots.

Most observers expect a delay of at least a few months while political parties prepare the groundwork of their campaigns, but experts say the new system is likely to benefit Sadr and his candidates.

On Friday, Sadr supporters carried Iraq's national tricolour and posters of the cleric, some of which evoked his past as a militia leader by depicting him in camouflage.

Volunteers dressed in light blue -- the movement's colour -- sprayed disinfectant from plastic tanks on their backs.

Sadr, who is very rarely seen in public, did not attend the rally.