Iraq's government on Saturday agreed a truce with the movement of Shi'ite cleric Moqtada al-Sadr to end weeks of fighting in an eastern Baghdad slum between Shi'ite militia and security forces, officials said.

The truce could end violence that has killed several hundred people, trapped the 2 million residents of Sadr City in a battle zone and prompted aid workers to warn of a humanitarian crisis.

But it is unclear how much control the anti-American Sadr has over many of the militiamen who claim allegiance to him in Sadr City, stronghold of his Mehdi Army.

"Prime Minister Nuri al-Maliki has approved this agreement," government spokesman Ali al-Dabbagh said. "The Iraqi government calls on all parties to commit to this deal, to be calm and show self-restraint."

The U.S. military said it was not aware of any agreement.

Sadr spokesman Salah al-Ubaidi told Reuters an agreement had been made between the Sadr movement's bloc in parliament and the ruling Shi'ite alliance, called the United Iraqi Alliance (UIA).

He said he expected the pact to take effect either on Saturday night or Sunday with a total halt to all Iraqi military activity for four days. He did not mention the U.S. military.

"The main aim of the deal is to solve the crisis in Sadr City," Ubaidi said.

Gunmen have been battling U.S. and Iraqi forces nearly every night in the slum since late March, when Maliki launched a crackdown on militias. Militants have also fired hundreds of rockets and mortars at the Green Zone government and diplomatic area in central Baghdad.

Ubaidi said that after the four-day ceasefire, Iraqi forces could enter Sadr City and detain anyone they wanted as long as they had an arrest warrant. He said the agreement called for aid to be delivered to residents and roads opened.

WILL FIGHTERS OBEY TRUCE?

Asked if Sadr's supporters would adhere to the agreement, Ubaidi said: "I expect they will. But look, the government has made promises before, but not fulfilled these promises. This may have an impact on the fighters."

Ubaidi said he expected Sadr to issue a statement ordering a halt to fighting. Sadr is believed to be in Iran taking advanced Islamic studies and has not been seen in public for a year.

Ali al-Adeeb, a member of Maliki's Dawa party, told Reuters there had been agreement that gunmen should lay down their arms and stop firing rockets and mortars at the Green Zone.

He added there had not been any discussion about dissolving the Mehdi Army, which Maliki has demanded.

The prime minister, himself a Shi'ite, has threatened to ban the Sadr movement from provincial elections in October unless the cleric disbands the Mehdi Army, which was blamed for stoking sectarian bloodshed in 2006 and 2007.

Sadr threatened last month to formally scrap a truce he imposed on the Mehdi Army in August unless the government halted its crackdown. A few weeks later he told the militia to observe the truce - which has at times seemed irrelevant - leaving Iraqis guessing over his true intentions.

Sadr backed Maliki's rise to power in 2006 but split with the prime minister a year ago when he refused to set a timetable for the withdrawal of U.S. forces from Iraq.