BAGHDAD, Iraq -- Five car bombs and two mortar rounds struck the capital's Shiite Sadr City slum Thursday, killing at least 161 people and wounding 257 police said. The attack by suspected Sunni Arab militants was the deadliest on a sectarian enclave since the war began and Shiites quickly struck back.

Soon after the onslaught, Shiite militants fired 10 mortar rounds at the Sunnis' holiest shrine in Baghdad, the Abu Hanifa mosque in the Azamiya neighborhood, killing one person and wounding 14. A 3-foot hole was blown in the dome and some inside rooms sustained severe damage.

Eight mortar rounds later slammed into the top Sunni organization in Iraq, the Association of Muslim Scholars, but caused no casualties, police said.

Fighting also flared in another part of Baghdad when 30 Sunni insurgents armed with machine guns and mortars attacked the Shiite-controlled Health Ministry. The attackers were repulsed after a three-hour battle, during which Iraqi soldiers and U.S. military helicopters intervened. At least seven ministry guards were wounded, police 1st Lt. Maitham Abdul-Razaq said.

The government ordered a curfew in Baghdad beginning at 8 p.m. Thursday, saying all people and vehicles must stay off the streets of the city until further notice. The government also closed Baghdad International Airport to all commercial flights, said Brig. Abdul-Karin Khalaf, the spokesman for the Interior Ministry.

Top officials held an emergency meeting at the home of Shiite leader Abdul-Aziz al-Hakim apparently to discuss deteriorating security. President Jalal Talabani, a Kurd; Vice President Tariq al-Hashimi, a Sunni; and U.S. Ambassador Zalmay Khalilzad attended, an aide to al-Hakim said.

Afterward, the three Iraqi officials appeared on national television, with al-Hashimi reading a statement urging calm and calling on politicians to work hard to reduce tensions that have brought a surge in sectarian bloodshed over the past year.

"We call for a revision of the government's existing security plans for Baghdad to better protect innocent civilians," he said.

Sectarian attacks and revenge killings have escalated since a bomb wrecked a Shiite shrine in Samarra last February.

Beginning at 3:10 p.m., three suicide car bombers blew up their vehicles one after another at 15-minute intervals in Sadr City, hitting the Jamila market, al-Hay market and al-Shahidein Square. At about the same time, two mortar rounds exploded at al-Shahidein Square and Mudhaffar Square, police Col. Hassan Challoub said.

Two other parked cars packed with explosives also blew up, one at the edge of Sadr City and another behind the main office of radical anti-American Shiite cleric Muqtada al-Sadr, Challoub said. A sixth car bomb was detected and detonated out of harm's way by police, he said.

Sadr City is the home of the Mahdi Army, the militia loyal to al-Sadr.

As the three fiery explosions sent huge plumes of black smoke over northeastern Baghdad and left streets covered with burning bodies and blood, angry residents and armed Shiite militiamen flooded the streets, hurling curses at Sunni Muslims and firing weapons into the air.

Ambulances raced to burning wooden fruit and vegetables stalls in Jamila market to rescue dozens of wounded. Rescue crews also removed burned bodies from mangled cars and minibuses and took them away on wheeled carts, but many corpses of adults and children remained in the streets.

Shortly after the attack, Mahdi Army militiamen deployed around the area, setting up checkpoints and roadblocks to keep all strangers away.

Challoub said the bombs and mortar shells killed 160 Iraqis and wounded 257.

The coordinated attack was the deadliest assault on a single Iraqi area since the U.S.-led war began in March 2003. The worst previous was a bombing in the southern city of Hillah that targeted mostly Shiite police and National Guard recruits in February 2004, killing 125 people and wounding more than 140.

There was a higher toll on March 2, 2004, but the attack occurred in two cities. Coordinated suicide bombings, mortar attacks and planted explosives struck Shiite Muslim shrines in Karbala and Baghdad, killing at least 181 Iraqis and wounding 573.

The fighting at the Health Ministry in northwest Baghdad began about noon, with heavy gunfire between 30 suspected Sunni insurgents and the building's guards, security officials said. Health Minister Ali al-Shemari is a follower of al-Sadr.

Iraqi troops rushed to the area and all roads leading to the ministry in the Bab al-Muadham neighborhood were closed, the security officials said, speaking on condition of anonymity because they were not authorized to speak to reporters.

Police Lt. Ali Muhsin said the attack began at 12:15 p.m. when three mortar shells hit the building, causing damage. After that, gunmen on the upper floors of surrounding buildings opened fire, he said.

Ministry workers were briefly trapped in the building.

"The gunmen fled as American helicopters and Iraqi armored vehicles arrived. Employees were able to leave starting about 3:15 p.m.," Health ministry spokesman Qassim Yehyah said.

Earlier Thursday, U.S. 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 in six days in which coalition forces have raided the district.

The militia is suspected of kidnapping U.S. soldier Ahmed Qusai al-Taayie, a 41-year-old Ann Arbor, Mich., resident as he was visiting his Iraqi wife in Baghdad on Oct. 23.

The Mahdi Army also is suspected of kidnapping dozens of people during the raid on a Ministry of Higher Education office in Baghdad on Nov. 14. The ministry is predominantly Sunni Arab.

In the raid on Sadr City at about 4:30 a.m., coalition troops searched houses and opened fire on a minivan carrying Iraqi workers in the al-Fallah Street area, killing four of them and wounding eight, police Capt. Mohammed Ismail said. He said the troops also detained five Iraqis.

In a statement, the U.S. military confirmed the raid and said it was conducted in the effort to find al-Taayie. It confirmed the detention of five Iraqis and said a vehicle was shot at by Iraqi troops after "displaying hostile intent." The statement did not report Iraqi casualties.

The U.S. military also issued a statement Thursday reporting three Marines were killed while fighting in Anbar province, where many Sunni Arab insurgents are based.

So far this month, 52 American military personnel have been killed or died.