Supporters of Iraqi cleric rally outside Baghdad's Green Zone

Amid heightened security, the crowds gathered outside the entry point of the Green Zone - which houses the Iraqi government - carrying and chanting pro-Sadr slogans.

The Iraqi security forces closed off entry points into the fortified zone early Friday and cut off main bridges leading to the fortified government and diplomatic compound in anticipation of the protests.

But thousands rallied outside the international zone in a show similar to that of last week's, when demonstraters in downtown Baghdad rallied against the government's stalled reform measures.

Sadr is a leading Shia cleric and whose followers formed militias against Sunni groups and the US-led occupation forces.

Anti-government protesters also took to the streets in the Shia majority provinces of Wasit, Babil and Karbala, a source told The New Arab.

Sadr addressed his followers through a televised speech, screened at the site of the rally.

Iraq's influential Shia cleric reiterated calls for government reform.

In anticipation of the demonstrations, Iraq security forces closed off entry points into the Green Zone on Friday [Getty]

"Your demonstrations today are not a security infringement," the cleric said addressing the crowd.

"We only seek to rid Iraq of the gang who are playing with people's lives and continue to rule over them without any right to do so."

Sadr had previously threatened to storm Baghdad's highly fortified Green Zone unless a new technocratic government was formed in the following 45 days.

The Iraqi government proposed a series of reform measures last year, following a nation-wide anti-corruption protests.

Iraqi Prime Minister Haider al-Abadi implemented initial reforms but has since failed to bring about tangible change.

He urged protesters to remain peaceful in a statement issued on Thursday night.

Special Forces and riot police were heavily deployed across the city, a military source told The New Arab.

As Iraq grapples with egregious corruption, officials from Sadr's own political movement have been accused of being some of the worst offenders.

The cleric has recently tried to distance himself from the Sadrist bloc.

Last Friday, he claimed that "none of the government members represent" him.

While Sadr has publicly criticised Abadi over the pace of reforms and his foreign policy, he has been generally more supportive of the premier than many other Shia factions in government.