Two suicide bombers blew themselves up Thursday in a crowded outdoor market in a Shiite city south of Baghdad, killing 61 people and wounding over 100, police said, the latest in a series of insurgent attacks against the majority sect during the Islamic holy month of Muharram.

The attackers strolled into the Maktabat outdoor market in the center of Hillah about 6 p.m. as shoppers were buying food for their evening meals. Police said they thought one of the men appeared suspicious and stopped him.

The bomber detonated his explosives, then the second attacker, who was walking behind the first, set off his, police added.

The attack killed 61 people and wounded 150, a local police spokesperson said.

Hillah, about 60 miles south of Baghdad, was the scene of one of the deadliest attacks in the war, when a suicide car bomber killed 125 people on Feb. 28, 2005.

The blast capped a day in which at least 17 other people were killed in bombings and mortar attacks against Shiite and Sunni targets in Baghdad as U.S. and Iraqi forces prepare for a security sweep to pacify the capital.

The unrelenting sectarian violence has taken on added significance this week as Shiites marked their holiest day on Tuesday — Ashoura — the 10th day of Muharram in the Islamic lunar calendar, when they mourn the death in A.D. 680 of the Prophet Muhammad's grandson, Imam Hussein. He was killed in Karbala as part of a power struggle that produced the split between Shiites and Sunni Muslims.

Complete coverage is available in FOXNews.com's Iraq Center.

A Foreign Ministry official said the government has invited neighboring countries, including U.S. rivals Iran and Syria, to a meeting on security next month in Baghdad. The official, who spoke on condition of anonymity because he wasn't authorized to disclose the information, did not give a specific date but said it was planned for March and would be the 10th held by Iraq's neighbors, but the first in the Iraqi capital. The last such meeting was held in July in Iran.

The government, meanwhile, said it would consider any attack against U.S. forces in this country as an assault against Iraq, but also wants good relations with its big eastern neighbor, Iran, underscoring the delicate balance it faces in keeping the rivalry between the two countries from spilling over its borders.

Spokesman Ali al-Dabbagh's comments came amid rising tensions between the United States and Iran, following the arrest of five Iranians in the northern Iraqi city of Irbil and the Jan. 20 attack to the south in Karbala in which four U.S. soldiers were kidnapped and slain. A fifth was killed in the raid.

Undersecretary of State Nicholas Burns said there was a "political and moral difference" between what the United States and the Iranians are doing in Iraq, reiterating allegations that Tehran has been supporting Shiite militias that have been blamed for much of the recent sectarian violence in Iraq.

"There's been increased evidence over that time that Iran has given this kind of assistance to the Shia insurgency groups in southern Iraq. They've attacked British soldiers near Basra, and they've now begun to mount those operations throughout the country, at least in the Baghdad region as well," he said in an interview with NPR.

A Foreign Ministry official, speaking on condition of anonymity because he was not authorized to disclose the information, said invitations to a meeting in March have been issued to Jordan, Kuwait, Iran, Saudi Arabia, Turkey and Syria, as well as Egypt, Bahrain, the Arab League, Organization of Islamic Conference and the United Nations.

Similar meetings have been held in recent years in Turkey, Iran and Egypt, but without any significant results. This would be the first to be held in Baghdad, the official said.

The announcement came a day after officials said Iraq has indefinitely halted all flights to and from Syria and closed a border crossing with Iran as the government prepares for a new U.S.-Iraqi security crackdown in the capital and surrounding regions.

In other violence Thursday, a car bomb exploded at a bus stop near a busy shopping area around Rusafi Square on Rashid Street in central Baghdad, killing six people and wounding 12, police said.

A bomb ripped the roof off a minibus in the predominantly Shiite neighborhood of Karradah, another popular capital shopping area, killing six people and wounding eight, police said, adding that the explosive was left in a bag by a passenger who got off the bus just before it detonated.

The blast sent up a plume of black smoke and devastated the blue-and-white bus, leaving charred seats jutting up from the twisted metal frame.

"We heard a big explosion and we rushed to the street to see the bus on fire and some wounded people jumping from the bus and falling on the ground," witness Jamal Ali said. "They were crying for help and some residents took them to the hospital without waiting for the ambulances. Only the driver was unhurt."

The bombings came hours after mortar rounds slammed into the Sunni neighborhood of Azamiyah for the third day in a row, killing five people and wounding 12, hospital and police officials said.

The mortars struck less than a mile from the revered Sunni Abu Hanifa mosque.

"What have we done to be attacked like this almost every day?" asked Saad Abdul-Karim, 50, whose son was wounded when their house was hit.

A U.S. soldier also died Thursday of wounds sustained in fighting two days ago in Anbar province, an insurgent stronghold west of Baghdad, the military said.

Complete coverage is available in FOXNews.com's Iraq Center.