The Iraqi government has welcomed the suspension by Shia cleric Moqtada al-Sadr of all armed actions by his Mehdi Army in a bid to remove rogue elements from the militia.
The move follows the deaths of 52 people in gun battles between Shia groups in the southern Iraqi city of Kerbala.
"All kinds of armed actions are to be frozen, without exception," a Sadr aide said.
An Iraqi national security adviser welcomed Sadr's suspension order but said it would need to be carried out. "If it happens it will reduce the violence in the country by a great deal," he said.
Aide to Shia cleric Moqtada al-Sadr
The battles on Tuesday appeared to pit Iraq 's two biggest Shia groups against each other - followers of Sadr and his Mehdi Army, and the rival Supreme Iraqi Islamic Council, whose armed wing controls police in much of the south.
"The aim is to remove bad members who are involved in the Mehdi Army and working for their personal interests . . . to hurt the Mehdi Army's reputation," another aide said.
Shia Prime Minister Nuri al-Maliki said militants involved in the violence in Kerbala wanted to blow up the Imam Hussein shrine, one of the holiest to Shia Muslims.
Analysts said the test of the six-month suspension order would be whether his fighters obeyed because it was no longer clear how much authority Sadr exercised over the Mehdi Army.
It is believed to have fragmented, and the US military says rogue factions receive funding, training and weapons from Iran. The Pentagon earlier this year called the Mehdi Army, which has thousands of gunmen, the greatest threat to peace in Iraq .
Sadr set up the Mehdi Army in 2003 after the US-led invasion of Iraq. A year later, he led his militia in two uprisings against US forces before getting involved in mainstream politics. He played a key role in Mr Maliki's rise to power in 2006.
In a split with Mr Maliki, Sadr withdrew his six ministers from the cabinet in April when the prime minister refused to set a timetable for the withdrawal of US troops from Iraq
While his ministers have left the cabinet, his political bloc holds 30 seats in parliament and is still part of the ruling Shia Alliance.
Mehdi Army fighters have avoided confrontation with US forces and kept a relatively low profile since the start of a large-scale security crackdown in February.