Thousands of Iraqis, mostly supporters of powerful cleric Muqtada Sadr, held a silent protest in central Baghdad on Friday, a week after a rally demanding electoral reform turned violent.

They gathered on Tahrir Square where on February 11 the security forces used rubber-coated bullets and tear gas to repulse protesters trying to march on the fortified Green Zone that houses the country's key institutions.

There was no violence on Friday and organisers asked the protesters to refrain from chanting slogans.

The demonstrators, waving Iraqi flags, remained completely silent for more than an hour, and many of them had taped their mouths.

Sadr supporters held a string of massive rallies last year, which on two occasions saw protesters break into the Green Zone, which is home to the country's key institutions as well as major Western embassies.

They have been demanding deep political reform since last year.

One of their demands includes reforming the current electoral system. The current seat allocation system for parliament was adopted before 2014 parliamentary polls, after small parties made significant gains in provincial elections a year earlier.

Security forces have been on high alert following last week's violence and a day after more than 50 people were killed in the deadliest car bomb explosion to hit the capital in months.

With provincial polls set for September, the protesters want an overhaul of the electoral law and the electoral commission to be replaced, on the grounds that both currently favour dominant parties they accuse of corruption and nepotism.