The fortified Green Zone came under fresh attack Monday, less than 24 hours after anti-American Shiite cleric Muqtada al-Sadr told his fighters to stand down following a week of clashes with government forces.

Al-Sadr's order stopped short of disarming his fighters and left the militia intact in a blow to the credibility of Prime Minister Nouri al-Maliki, who flew to the southern oil city of Basra a week ago to personally oversee a crackdown on militia violence.

The Shiite leader promised "a decisive and final battle" but made little headway. A key adviser to al-Maliki said the operations against al-Sadr's followers would end within days.

"Before the end of this week, the operations will come to an end and Prime Minister Nouri al-Maliki will be back to Baghdad," the adviser, Sami al-Askari, said.

Iraqi government spokesman Ali al-Dabbagh said, however, that "operations will not end until Basra reaches a secure and acceptable situation enabling Iraqi citizens to live normal and secure lives."

He did not elaborate on how long that might take.

Defense Secretary Robert Gates said Monday that al-Maliki was to be commended for taking the initiative in Basra, and he described the Iraqi security forces as having performed reasonably well, with American support.

"Based on what I've seen, the limited reporting I've seen ... they seem to have done a pretty good job," Gates said, speaking to reporters traveling with him in Europe.

"We've all known that at some point the situation in Basra was going to have to be dealt with," Gates said. "It is the economic lifeline of the country and been under the control of a bunch of thugs, gangs (and) militias. Over the long term it's unacceptable."

The rocket or mortar attacks on the nerve center of the U.S. mission and the Iraqi government continued more than a week of near-daily fire mostly from Shiite-dominated areas of eastern Baghdad.

The number of rounds going into the zone has dropped in recent days, but the continuing attacks indicate that al-Sadr may not be able to reign in all Shiite militia factions.

The U.S. Embassy said no serious injuries were reported and the U.S. military said it had no reports of major damage. At least two Americans working for the U.S. government died in attacks on the zone last week.

Separately, an American soldier was killed by a roadside bomb in northeast Baghdad on Monday, the military announced. It was unclear whether the attack was carried out by Shiite or Sunni militants.

The clashes between Shiite militias and Iraqi troops backed by U.S. forces began last Tuesday, when al-Maliki launched military operations against the group and vowed to remain in Basra until the mission was accomplished. The battles there and violence that spread to other southern cities and Baghdad killed at least 400 people.

Al-Sadr's cease-fire call followed intense negotiations by Shiite officials, including two lawmakers who traveled to Iran to ask religious authorities there to intervene, according to Iraqi officials familiar with the negotiations.

Lebanon's top Shiite Muslim cleric issued a religious edict Monday banning attacks on public utilities in Iraq, mainly the oil industry, urging Iraqis to solve their problems through dialogue. Two oil pipelines have been attacked in Basra over the past week.

Iraqi-born Grand Ayatollah Mohammed Hussein Fadlallah, who enjoys some influence among Iraq's Shiites, said "it is prohibited to attack properties and public wealth, whether it is oil wealth or other types of wealth, and attacks on people, their lives, security, stability, property or honor."

The situation in Basra, 340 miles southeast of Baghdad, was relatively calm on Monday, although sporadic gunfire could still be heard in the streets and AP Television News footage showed Iraqi troops searching house-to-house apparently targeting militants.

Some supermarkets and stores were open but residents said few people were venturing out.

A citywide curfew was lifted in Baghdad, although a vehicle ban remained on three strongholds of al-Sadr's Mahdi Army militia in the capital.

Sadr City, the Shiite neighborhood where many of the mortars and rockets landing in the Green Zone are believed to be launched, was calm, residents said. Cars and buses were moving within the sprawling area, though they weren't allowed to leave.

In other parts of Baghdad, shops and schools were open and people were heading to work.

Al-Sadr's order was announced Sunday after lawmakers Hadi al-Amri and Ali al-Adeeb reportedly asked Iranian authorities to stop the flow of weapons to al-Sadr's Mahdi Army as well as groups closely allied with the Americans. Tehran denies that it backs Iraqi militias.

The lawmakers — both of whom have close ties to Iran — also asked the Iranians to pressure al-Sadr to come up with a face-saving initiative, according to Iraqi officials, who spoke on condition of anonymity because of the sensitivity of the subject.

Near Buhriz, about 35 miles north of Baghdad, unknown gunmen in a car attacked a checkpoint manned by U.S.-backed Sunni fighters, police said. Four of the fighters were killed.