Sunni-led insurgents killed at least 10 people with a car bomb in a crowded vegetable market Friday, the Muslim day of worship, in the second blast against Shiite civilians in as many days, police said. The death toll rose to 102 from the previous day's attacks in another Shiite town.

Elsewhere, in the southern city of Basra (search), a police convoy was ambushed late Thursday, killing four policemen and wounding one, said Capt. Mushtaq Khazim.

Iraqi security forces also captured a woman wearing explosives hidden under her clothes headed for a crowded weekly flea market in Baghdad (search) on Friday, an Iraqi general said. The discovery came two days after the first known blast by a female homicide attacker in Iraq, which raised fears of a new insurgent strategy.

Sunni militants have launched a bloody new surge of violence to wreck an Oct. 15 referendum on a new constitution — targeting the Shiite majority, which now dominates Iraq's (search) government. At least 198 people, including 13 U.S. service members, have been killed in the past five days.

Al Qaeda in Iraq, the country's most feared insurgent group, has declared "all-out war" on Shiites. But the style of Thursday's and Friday's attacks indicated some other group may have carried them out. Nobody immediately claimed responsibility for either, and both explosions included parked car bombs. Al Qaeda traditionally relies on homicide bombers and quickly claims its operations.

Moderate Sunni Arab leaders have urged their community to reject the constitution, saying it will fragment Iraq and leave them weak, compared with Shiites and Kurds. Passage of the charter is key to prospects for starting a withdrawal of American troops — and if it fails, the country's political instability will deepen.

The bombing attacks in the two mainly Shiite towns, Hillah and Balad, appeared aimed at killing as many civilians as possible.

Friday's car bomb exploded at 9:30 a.m. in the Souq al-Sharia, an outdoor vegetable market bustling with shoppers, about 200 yards from the provincial governor's office in Hillah, 60 miles south of Baghdad. At least 10 people, including three women and two children, were killed and 41 were wounded, said Dr. Mohammed Beirum of Hillah General Hospital.

As Iraqi police and soldiers sealed off the market, emergency workers lifted the wounded and dead into ambulances from streets covered with pools of blood and debris.

In Iraq, the weekend is Friday and Saturday, and before heading to services in mosques at midday Friday, the Muslim day of worship, many Iraqis shop in their local markets.

Jawad Khazim, 45, who witnessed the Hillah attack, said he was temporarily deafened by the explosions. "I saw a fireball rising from the marketplace, and vegetables and human flesh flying through the air," he said.

He condemned the insurgents for trying to kill Shiites and questioned why they would target a crowded marketplace where minority Sunnis and Christians could also be.

The Balad attack came Thursday just before sunset, 50 miles north of the capital. A homicide bomber drove his car into the town's outdoor produce market, detonating it, followed moments later by an explosion of a car parked at a nearby bank. Another parked car exploded on Bint al-Hassan Street, a busy commercial avenue, said police chief Col. Kazem Abdul-Razaaq. He was wounded in the blasts, along with four other police rushing to the scene of the first explosion.

At least 102 people were killed, including 13 children and four women, and 150 were wounded, said Dr. Khaled al-Azzawi of Balad hospital. An unspecified number of Sunnis who run some of the stands in the market were among the victims.

Insurgents simultaneously hit a police checkpoint elsewhere in the city with six mortar rounds, killing a civilian. U.S. soldiers based there returned the fire and detained an Iraqi suspect from a nearby home after finding traces of explosives on his body, the military said.

Also Thursday, the U.S. military announced the deaths of five U.S. soldiers a day earlier in a roadside bombing during combat in Ramadi, west of Baghdad, a hotbed of Iraq's insurgency.

It was the deadliest single attack against American troops in more than a month, bringing to 1,934 the number of U.S. service members who have died since the war started in March 2003, according to an Associated Press count.

The woman who was strapped with explosives was intercepted as she was headed for Souq al-Haraj, a weekly Friday market, said Iraqi army Gen. Jalil Khalaf. She was arrested and was being interrogated, he told the AP, without elaborating.

In Washington, the top American commander in Iraq said Thursday that the process of withdrawing U.S. troops depends greatly on the referendum results and elections set to follow if the constitution passes. "The next 75 days are going to be critical," Gen. George Casey told the Senate Armed Services Committee.

Sunnis make up only 20 percent of Iraq's population of some 27 million, but they could defeat the charter because of a loophole in voting rules: If two-thirds of voters in any three of Iraq's 18 provinces vote "no," the referendum fails — even if an overall majority approves. Sunnis could potentially cross that margin in four provinces.

Sunni leaders complain the constitution does not emphasize Iraq's unity and Arab character. They say its federal system — which would allow Shiites in the south and Kurds in the north to form mini-states — will leave Sunnis in a weak middle region, cheated of oil resources.

U.S. Ambassador Zalmay Khalilzad has been struggling to negotiate changes to the charter in hopes of winning Sunni Arab support, and senior U.S. officials in Washington have said they are confident that Iraq's draft constitution will be approved.