A driving ban brought the Iraqi capital a day of relative calm, a rare period of peaceful streets enforced, in part, by a Shiite Muslim militia - one of several armed groups the US military wants abolished. Thousands of Shiites - frisked by Mahdi Army militiamen in yellow button-down collar shirts and armed with Kalashnikov rifles and metal detector wands - knelt in prayer at a huge outdoor service in Baghdad's Sadr City slum. The militia that kept order Friday was the same force that went on a rampage of reprisal attacks against Sunni Muslim mosques and clerics after the February 22 bombing of a Shiite shrine in Samarra. Thursday night, after a deadly bomb attack in the poor Shiite neighborhood, police and aides to anti-American cleric Muqtada al-Sadr announced the radical leader's militia, the Mahdi Army, would help government security forces patrol Sadr City. The government decision to legitimize joint patrols with the Mahdi Army - which had been going on anyway - appeared to have tacit US military approval, even though American forces have fought several protracted battles with the Shiite fighters for control of southern holy cities and the Sadr City Shiite stronghold. Acceptance of the higher profile for the Mahdi Army, if only for a time, signaled the extreme importance US authorities have put on quelling more than a week of deadly sectarian violence after the Samarra bombing. The Americans took pains to stay out of the conflict - but there was criticism, nevertheless. Abdul-Salam Al-Kubaisi, a spokesman for the Sunni clerical Association of Muslim Scholars, suggested US Ambassador Zalmay Khalilzad might share blame for the violence along with some Shiite religious leaders. Two days before the gleaming dome atop the 1,400-year-old Askariya shrine was bombed, Khalilzad had warned that the United States would not continue to support institutions run by sectarian groups with links to armed militias. Sunnis accuse Shiite militiamen operating in the ranks of the Interior Ministry, which controls the police, of widespread abuses. In a teleconference briefing with reporters in Washington on Friday, the US commander in Iraq, Gen. George W. Casey, said he believed "the crisis has passed." He added that the militias were "a long-term challenge, a long-term problem and there's no silver-bullet." Casey said the military hoped some militia members would, over time, be integrated into the Iraqi government forces. "What we find is that, with the right leadership, even if someone has been a member of a militia, they generally respond favorably and work to support the unit's efforts." The spasm of violence after the Samarra bombing has further tangled negotiations to form a government and, as a result, threatened American hopes of starting a troop pullout this summer. Sunni, Kurdish and some secular politicians have launched a campaign to deny Shiite Prime Minister Ibrahim al-Jaafari a second term. Nevertheless, Casey said he still planned to issue an assessment this spring on the possibility of starting to withdraw US forces. The Friday lull in violence followed a night of carnage in two southeastern Baghdad suburbs, where some 50 gunmen stormed an electricity substation and a brick factory nearby where they slaughtered Shiite factory workers in their sleep, police said. The attacks raised Thursday's death toll to 58. In much of the country Friday, worshippers walked in peace to mosques to offer prayers and listen to sermons, in which some imams - both Shiite and Sunni - called for unity and an end to violence. "There is no difference between Sunni and Shiite," Sheik Hadi al-Shawki told Shiite worshippers in Amarah, 180 miles (290 kilometers) southeast of Baghdad. "We have to unite and not let the terrorists divide us." But anger at the Americans and the Iraqi government found its way to pulpits on both sides of the Shiite-Sunni divide. In Samarra, 60 miles (96 kilometers) north of Baghdad, thousands of Sunnis gathered in the Grand Mosque, spilling into the streets and courtyard around the nearby Askariya shrine. Cleric Ahmed Hassan al-Taha accused US forces and their allies of stoking the tension between majority Shiites and minority Sunnis. "Iraqis were living in harmony until the occupiers and those who came with them arrived in this country. They are responsible for igniting sectarianism," al-Taha said. Hundreds took to the streets after services in the southern Shiite stronghold of Basra and marched to the Iraqi South Oil Co., threatening to disrupt exports unless the government provides better protection and greater support to local authorities and private militias. Security forces sealed off Baghdad, preventing most vehicles from entering or leaving the city of 7 million. Armed police and soldiers in bulletproof vests manned checkpoints across the capital, preventing most cars and motorcycles from leaving their neighborhoods. Downtown was largely deserted. Most shops and gas stations were closed, though small groceries were open. Dozens of young boys turned parts of Baghdad's usually busy Saadoun Street into improvised soccer fields, looking clearly unhappy when the odd car disrupted their games. A daytime curfew and vehicle restrictions last weekend helped curb the worst of the sectarian killings, but attacks resumed this week. In scattered attacks Friday, a mortar shell slammed into a market south of Baghdad, killing one person and wounding another. And police found three handcuffed, blindfolded, bullet-riddled bodies across the country.