Several thousand supporters of populist Iraqi cleric Moqtada al-Sadr demonstrated in central Baghdad on Friday, calling for reforms that politicians have been quick to promise but slow to carry out.

Iraq's government is mired in corruption, struggles to provide basic services, and positions have for years been shared out based on political and sectarian quotas that protesters have demanded be scrapped.

Friday's demonstration had a festive atmosphere, with protesters at Tahrir Square in central Baghdad waving flags, dancing to pro-reform songs and chanting slogans calling for change.

"The government is not serious," Kadhim Hussein, a 41-year-old labourer, told AFP.

"They made some changes but the most corrupt are still here. They must all go," he said.

Sadr's movement this week called for a mass demonstration on Friday following a lull in what were weekly protests earlier this year.

The demonstration was peaceful, with security checks performed by members of the Sadrist movement and police forces deployed in smaller numbers than on previous occasions.

Protests in central and southern Iraq broke out in the summer of 2015 calling for improvements to abysmal services, a platform that later expanded to include curbing corruption and implementing reforms.

The initial protests fell off, but the movement was revitalised earlier this year by Sadr, who drew on his wide support base to stage mass demonstrations.

Protesters broke into the fortified Green Zone several times, storming parliament and the prime minister's office.

Security forces later took a harder line, causing several deaths and injuries as they dispersed protesters.