Sadr's statement was the result of behind-the-scenes talks between the Sadrists and the ruling Shi'ite Alliance mediated by former Prime Minister Ibrahim Jaafari, Shi'ite politician Ahmed Chalabi and Sunni Arab parliament speaker Mahmoud Mashhadani.
Chalabi told Reuters Sadr's statement was "the key to stopping the bloodshed in Basra" but the government also had to stop targeting Sadrists.
In his statement, Sadr called for an end to "random arrests" of his followers and for them to benefit from an amnesty law passed by parliament in February aimed at freeing thousands of prisoners from Iraqi jails.
The government welcomed Sadr's statement but said it would press on with its campaign for control over Basra, which is divided up among various militias and criminal gangs.
"The statement by Moqtada al-Sadr is a step in the right direction," Maliki said.
Government spokesman Ali al-Dabbagh said the operation would continue "until it achieves its goals". He said Iraqi troops focused on hunting down criminals, not Sadrists.
Scores of people have been killed in clashes in southern Iraq and in Shi'ite neighbourhoods of Baghdad.
Authorities lifted an indefinite curfew in Baghdad with effect from 6 a.m. (4 a.m. British time) on Monday. Cars remain banned in three districts, however.
Maliki, in Basra to oversee the six-day-old operation, has given Shi'ite fighters until April 8 to turn over their weapons in return for cash.
Sadr aide Hazem al-Araji told journalists: "The weapons of the resistance will not be delivered to the Iraqi government."
Shortly after Sadr's statement, a salvo of rockets or mortars was fired at the Green Zone diplomatic and government compound in central Baghdad. The U.S. military has blamed rogue Mehdi Army militiamen for similar barrages in the past week.
But in Nassiriya a Reuters reporter said clashes had stopped and Mehdi Army fighters were seen withdrawing from the streets.
In Basra, there were sporadic clashes in the old city but otherwise there appeared to be a lull in the violence, a Reuters reporter said. An official in Sadr's office there, Ali al-Sinidi, said the cleric's order was being implemented.
Iraqi government forces have struggled to drive well-armed Mehdi Army fighters off the streets of Basra and British and U.S. forces have had to intervene.
