The enormous turnout came despite scorching heat and the Shiite cleric not being there in person -- an indication of his status as a political heavyweight, as well as a key religious authority.

The midday prayer, on Al-Falah Avenue in Sadr City, was instead led by a Sadr ally who took aim at rivals from other Shiite factions, including a powerful ex-paramilitary network.

"We are at a difficult... crossroads in the formation of the government, entrusted to some we do not trust," said Sheikh Mahmud al-Jayashi, reading Sadr's sermon.

Some factions have shown themselves to "not be up to the task", he contended.

Sadr's bloc won 73 seats in the October 2021 election, making it the largest faction in the 329-seat parliament.

But since the vote, talks to form a new government have stalled and the oil-rich country remains mired in a political and socioeconomic crisis, despite elevated global oil prices.

The various Shiite political factions, representing Iraq's largest demographic, remain unable to agree on a new prime minister.

Sadr initially supported the idea of a "majority government" which would have sent his Shiite adversaries from the pro-Iran Coordination Framework into opposition.

The former militia leader then surprised many by compelling his deputies to resign from parliament in June, a move seen as seeking to pressure his rivals to fast-track the formation of a new government.

- Taking aim at Hashed -

But a month later, the process has not advanced.

Sadr's sermon took particular aim at the Hashed al-Shaabi, a Shiite former paramilitary force that has been integrated into the army, but is seen by many Iraqis as an Iranian proxy.

The Hashed "must be reorganised and undisciplined elements must be removed", the preacher said, lamenting "foreign interventions" but without naming any country.

He also called for the Hashed -- whose political wing is part of the Coordination Framework -- to be kept at "a distance from politics and business".

Before the prayer began, Sadr loyalists expressed support for the cleric with cries of "Yes, yes to reform! Yes, yes to the reformer!"

Some held prayer mats in hand or waved Iraqi flags.

"We obey Moqtada Sadr, as we obey God and his prophets," Sheikh Kadhim Hafez Mohammed al-Tai told AFP at the rally in Sadr city.

After the 2003 US invasion that toppled dictator Saddam Hussein, the district of the capital was named after Mohammad Sadr, Moqtada's father, a cleric who was assassinated in 1999 under Saddam's rule.

The Friday prayers were ostensibly organised as a tribute to Sadr's father.