"We are one tribe and our leader is Moqtada Sadr!" chanted a crowd of men on Friday in Tahrir Square, the main gathering place in Iraq's capital for rival anti-government rallies.

Sadr, who has a cult-like following across Iraq, first backed the popular protests when they erupted in October but has since split with them over the appointment of a new prime minister.

The cleric backs Mohammad Allawi, a premier-designate rejected by most demonstrators as too close to the ruling class they have railed against for months.

Over the last two weeks, Sadr has sought to clamp down on the main movement and his followers have attacked rival demonstrators.

In another twist, the cleric published a series of guiding principles for protesters this week, including separation of the sexes and banning drugs or alcohol.

"We will not stay with arms crossed, silent in the face of insults against religion, morality and country," Sadr said.

Many have long been afraid to criticism the militiaman-turned-politician because of his influence, but his comments on Twitter were met with outrage and mockery.

On Friday though, Sadrists held counter-protests in Baghdad, the southern port city of Basra and the shrine city of Najaf, rejecting criticism of their leader.

"We reject agitators who sneak in among the protesters, shattering the movement's peaceful nature and insulting prophets and religious symbols," one Sadrist told AFP.

There were no clashes between the Sadr supporters and the anti-government demonstrators, but previous clashes between the two have left eight activists dead.

Around 550 people have been killed since the rallies erupted four months ago and another 30,000 wounded.

Incoming premier Allawi has until March 2 to form his new cabinet, which would need a vote of confidence from Iraq's divided parliament.

His government is expected to steer Iraq into early legislative elections, a key demand of protesters.