Suicide bombings and mortar attacks killed at least 161 people and wounded 257 Thursday in Sadr City, Baghdad's Shiite slum, Iraqi police confirmed.

Following one of the worst days of violence since the start of the Iraq war, an indefinite curfew has been slapped on Baghdad.

The Sadr City attacks, which occurred in 15-minute intervals, involved three suicide car bombs and two mortar rounds.

The first blast occurred around 3:10 p.m., killing about 10 people at Jamila vegetable market. The next occurred 15 minutes later at al-Hay market and then at al-Shahidein Square in Sadr City.

Around the same time, mortar rounds struck al-Shahidein Square and Mudhaffar Square, confirmed police.

Col. Hassan Chaloub said many outdoor stalls, automobiles and buses were destroyed in the multiple attacks.

Brig. Gen. Abdul-Karim Khalaf, a spokesman for the Interior Ministry, told state-run Iraqiyah television that police captured another would-be car bomber and that three other failed bombers were on the run. Khalaf released the license plate numbers of each car and asked the public to notify police if they saw them.

Sadr City is known as the home of the Mahdi Army -- a militia loyal to radical anti-American Shiite cleric Muqtada al-Sadr.

Quickly on the heels of the attack in Sadr City came the attack in northeastern Baghdad, where Shiite militia launched 10 mortar rounds at the Abu Hanifa Sunni mosque.

Residents and armed militiamen took to the streets shouting curses at Sunni Muslims while firing weapons in the air.

The retaliation killed one person and wounding 14 in the attack on the holiest Sunni shrine in Baghdad.

Sectarian fighting also occurred in another part of northern Iraq Thursday as 30 Sunni insurgents attacked the Shiite-controlled Health Ministry using machine guns and mortars.

The battle lasted three hours and ended only after the involvement of Iraqi soldiers and U.S. military helicopters. Seven ministry guards were wounded, said police 1st. Lt. Maitham Abdul-Razaq.

Earlier Thursday, U.S. and Iraqi forces killed four Iraqis during a sweep through an area of Sadr City in a search for a kidnapped American soldier.

The raid was the fourth in six days undertaken by coalition forces in Sadr City.

The Mahdi Army is suspected of kidnapping U.S. soldier Ahmed Qusai al-Taayie, a 41-year-old soldier kidnapped while visiting his Iraqi wife in Baghdad on Oct. 23.

The militia is also suspected of being behind the Nov. 14 raid on the Ministry of Higher Education office in Baghdad, in which scores of Sunni Arabs were kidnapped.

Also Thursday, the U.S. military said three Marines were killed in fighting in Anbar province, the home to many Sunni-Arab insurgents. The three dead bring the American service member death toll to 52 in November.

The Sadr City attack was the deadliest assault on a single Iraqi area since the U.S.-led war began in March 2003.

Prior to the Sadr City attack, the worst previous was a bombing in the southern city of Hillah that killed 125 people and wounded 140 in a targeted mission against Shiite police and National Guard recruits.

A higher toll of 181 Iraqis was recorded on March 2, 2004, but the attack occurred in two cities -- Baghdad and Karbala.

The ongoing sectarian violence between Sunnis and Shiites has plunged Iraq into what many analysts consider a civil war-type environment.

Thursday's events prompted top officials to hold 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, confirmed an aide to al-Hakim.

With files from The Associated Press