The Shiite preacher's Marching Towards Reform alliance scooped 54 seats in an upset at May 12 polls to become the biggest bloc in Iraq's 329-seat parliament.

But Sadr -- whose militia battled American troops after the 2003 US-led invasion -- faces a mammoth task to stitch together a working majority as his demands for less foreign influence in Iraq have stirred tensions with both Washington and Tehran.

In a bid to jumpstart negotiations, Sadr met over the weekend with Prime Minister Haider al-Abadi, whose group finished third, and Hadi al-Ameri, whose bloc of pro-Iranian former fighters came second.

After the meetings, the cleric urged "the formation of an inclusive government as quickly as possible" and called for a "nationwide political decision", his office said in a statement Sunday.

Sadr -- whose fighters were once accused of sectarian killings -- has reinvented himself as an anti-graft crusader looking to bridge Iraqi society in alliance with secular leftists.

The election saw a record number of abstentions as Iraqis snubbed the corruption-tarnished elite that has dominated the country since the 2003 toppling of Saddam Hussein.

It is still far from certain that Sadr, who has ruled himself out of becoming the new premier, will be able to ensure his bloc comes to power.

Whoever emerges at the helm will face the huge job of rebuilding a country left shattered just five months after the defeat of the Islamic State group.