Shi'ite militiamen grabbed six Sunnis as they left Friday worship services, doused them with kerosene and burned them alive near an Iraqi army post. The soldiers did not intervene, police Capt. Jamil Hussein said. The savage revenge attack for Thursday's slaughter of 215 people in the Shi'ite Sadr City slum occurred as members of the Mahdi Army militia burned four mosques, and several homes while killing an unknown number of Sunni residents in the once-mixed Hurriyah neighborhood. Gunmen loyal to radical anti-American Shi'ite cleric Muqtada al-Sadr began taking over the neighborhood this summer and a majority of its Sunni residents already had fled. On Thursday Sunni insurgents blew up five car bombs - three of them suicide attacks - in Baghdad's Shi'ite Sadr City slum, killing at least 215 and wounding 257 in an act of carnage that sent the US ambassador racing to meet with Iraqi leaders and moved Iraq a step closer to all-out civil war. Shi'ite mortar teams quickly retaliated, firing 10 shells at Sunni Islam's most important shrine in Baghdad, badly damaging the revered Abu Hanifa mosque and killing one person. Eight more mortar rounds slammed to earth near the west Baghdad headquarters of the Association of Muslim Scholars, the top Sunni Muslim organization in Iraq. Nearby houses were set on fire but there were no immediate reports of casualties. Two other mortar barrages on Sunni neighborhoods in west Baghdad killed nine and wounded three, police said late Thursday. The attacks stood to further snarl decision making in Washington, where there were indications the Bush administration was preparing an accelerated hand-over of security responsibilities to Iraqi forces. Thursday's mass killings only emphasized the impotence of the Iraqi army and security forces in the face of determined sectarian attackers. "We condemn such acts of senseless violence that are clearly aimed at undermining the Iraqi people's hopes for a peaceful and stable Iraq," Jeanie Mamo, a White House spokeswoman, said. Bush and Prime Minister Nouri al-Maliki were already slated to meet next week in Amman, Jordan. The government imposed a curfew on the capital and closed the international airport until further notice, and leaders of Iraq's Shiite, Sunni and Kurdish communities issued a television appeal for calm after a hastily organized meeting with US Ambassador Zalmay Khalilzad. The American Embassy said it had nothing to report about the session. Later Thursday the transport ministry took the highly unusual step of also closing the Basra air and sea ports until further notice, virtually sealing the country. Basra is Iraq's second largest city and its main window to vital shipping lanes in the Gulf. Al-Maliki, a Shi'ite, went on state television and blamed Sunni radicals and followers of Saddam Hussein for the attacks. Hospital corridors and waiting rooms in Sadr City hospitals were awash in blood and mangled survivors of the quintuple attacks that struck at 15 minute intervals in the Shi'ite district _ stronghold of the Mahdi Army militia of radical anti-American cleric Muqtada al-Sadr, a key al-Maliki backer. The militia and associated death squads are believed responsible for the murders of hundreds of Sunnis since suspected al-Qaida in Iraq operatives bombed an important Shi'ite shrine in Samarra, north of Baghdad, in February. Al-Maliki associates, speaking to The Associated Press on condition of anonymity because of the sensitive nature of the information, said the prime minister was deeply afraid that al-Sadr would no longer be able to hold back his heavily armed fighters from a renewed and furious round of revenge attacks. In a television statement read by an aide, Al-Sadr urged unity among his followers to end the US "occupation" that he said was causing the strife. Al-Sadr said the attacks coincided with the 7th anniversary of the assassination of his father, Mohammed Sadiq al-Sadr, a revered Shi'ite religious leader. The anniversary reckoning was by the Islamic calendar. "Had the late al-Sadr been among you he would have said preserve your unity," Muqtada al-Sadr said. "Don't carry any act before you ask the Hawza (Shiite seminary in Najaf). Be the ones who are unjustly treated and not the ones who treat others unjustly." Grand Ayatollah Ali al-Sistani, the pre-eminent Shi'ite religious figure in Iraq, condemned the attack and issued condolences to family members of those who were killed. He called for self-control among his followers. Huge columns of black smoke rose into low-hanging clouds above the sprawling and ramshackle district. Twisted and charred cars and buses littered the blood-smeared streets where the bombers attacked as markets were jammed with shoppers buying supplies on the eve of Friday's Muslim day of rest and prayer. Iraq is suffering through a period of unparalleled violence. The United Nations reported only a day before the horrendous Sadr City attack that 3,709 Iraqi civilians had been killed in October, the most in any month since the war began 44 months ago, and a figure that was certain to be eclipsed in November. In a sign that the sectarian skirmishing in Iraq was headed into civil war, the Sadr City slaughter occurred just moments after US helicopters and Iraqi armor had to move into to stop an attack by 30 masked Sunni gunmen who were trying to storm the Shi'ite-dominated Health Ministry, about a mile west of the Shi'ite slum. Seven ministry guards were wounded. Residents also reported heavy mortar fire and gunbattles in Hurriyah, a now-largely Shi'ite neighborhood in northwest Baghdad. There were pitched battles between gunmen and the army on Haifa Street, a dangerous thoroughfare running north from the Green Zone, site of the American and British embassies as well as the Iraqi government and parliament. Iraqis also reported heavy fighting around the Jadriyah Bridge near Baghdad University and AP personnel saw 12 pickup trucks loaded with men armed with rocket-propelled grenade launchers and heavy machine guns driving through the center of the city unaccosted. Counting those killed in Sadr City, a total of at least 213 people died or were found dead across Iraq on Thursday. Before dawn Thursday, US and Iraqi forces searching for a kidnapped American soldier swept through an area of Sadr City, killing four Iraqis, wounding eight and detaining five, police said. The raid was the fourth time in six days that coalition forces have raided the district looking for kidnapped US soldier Ahmed Qusai al-Taayie, a 41-year-old Ann Arbor, Michigan, resident who was snatched from the street while he was visiting his Iraqi wife in Baghdad on Oct. 23. The Mahdi Army was believed to have grabbed al-Taayie as well as scores of people during the raid on a Ministry of Higher Education office in Baghdad on Nov. 14. The ministry is predominantly Sunni Arab. During the 4:30 a.m. raid coalition forces searched houses and opened fire on a minivan carrying Iraqi workers in the al-Fallah Street, killing four of them and wounding eight, said police Capt. Mohammed Ismail. Iraqis often use the crowded communal taxis to travel early in the morning to sites where they hope to get work as day laborers. Ismail said coalition forces also detained five Iraqis. In a statement, the US military confirmed the raid and said it was conducted in the continuing effort to find al-Taayie. It confirm the detention of five Iraqis and that a vehicle was shot at by Iraqi forces after "displaying hostile intent." But the coalition did not report Iraqi casualties. The military also reported the deaths of three Marines who were killed while fighting in Anbar province, where many Sunni-Arab insurgents are based. So far this month, 52 American service members have been killed or died.