Apparently seeking to calm fears that he will not go after militia gunmen loyal to one of his key political backers, Prime Minister Nouri al-Maliki said 400 fighters from the Mahdi Army had been arrested over the past several weeks.

In Baghdad on Thursday, bombers and gunmen killed at least 19 more people in a series of attacks in the pre-noon hours as the capital faces a surge in violence ahead of a planned U.S.-Iraqi security crackdown.

It was the first time the Shiite prime minister has specifically detailed any arrests of figures from the Mahdi Army militia that is loyal to his key backer, the radical cleric Muqtada al-Sadr. Many of the militiamen are believed responsible for a majority of the sectarian violence in Baghdad over the past year.

• Visit FOXNews.com's Iraq Center for more in-depth coverage.

Yassin Majid, a senior al-Maliki adviser, said reports that dozens of senior militia leaders had been detained were incorrect.

A Baghdad Mahdi Army commander, meanwhile, said U.S. and Iraqi troops launched a major campaign Tuesday in Um al-Maalef, a Shiite neighborhood in south Baghdad.

"They detained every man who was able to carry weapons. We heard from our people in the area that about 400 people were detained," said the militia commander on condition of anonymity because senior figures in the group are not permitted to give their names.

He said that in December U.S. troops had killed one of the Mahdi Army's top commanders, known as Abu al-Sudour, in Sadr City.

Meanwhile, the Italian daily Corriere della Sera reported Thursday that al-Maliki was deeply critical of President Bush during a briefing with a small group of reporters.

"The situation would be much better if the United States had immediately sent our security forces more adequate weapons and equipment. If they had committed themselves more and with greater speed we would have had a lot fewer deaths among Iraqi civilians and American soldiers," al-Maliki was quoted as saying by Corriere.

However, the premier stopped short of openly criticizing Bush's plan to send 21,500 more troops to join the estimated 130,000 already there.

"We have to see how the situation in the field will go," he said. "We cannot rule out that the situation will drastically improve, allowing U.S. troops to leave the country in great numbers in three to six months."

The newspaper quoted the embattled Iraqi leader as saying Bush had capitulated to domestic pressure when he criticized the hanging of former leader Saddam Hussein. He further struck back at comments by Secretary of State Condoleezza Rice which suggested al-Maliki was in a weak position and on borrowed time.

He said such remarks were giving aid and comfort to militants fighting to drive out American troops and unseat his government.

In the deadliest attack on Thursday, three car bombs detonated within minutes of each other in front of a wholesale vegetable market near a Shiite enclave on the edge the predominantly Sunni neighborhood of Dora in southern Baghdad, killing at least 10 people and wounding 30, police said.

The force of the 10:20 a.m. blast blew off part of the metal roof covering a loading area and a burned out van still had its bundle of lettuce and onions tied to the top. Associated Press Television News footage also showed the charred hulk of a car wedged under a truck. Lettuce and bloodstained clothes were scattered on the ground.

The al-Rashid market is located near Dora's Abu Dishir area on the highway that links the capital with the Iraq's southern areas. Most of the shop owners and workers were Shiites from Abu Dishir, although some Sunni vendors also use the market.

"I will think twice before transporting goods to this market again," said a driver from Hillah, a predominantly Shiite town 60 miles south of Baghdad, who identified himself only as Hussein.

About an hour later, a parked car bomb also struck a religiously mixed commercial area on a busy thoroughfare in central Baghdad, killing four people and wounding 10 others. The blast burned many civilian cars and shattered the windows of nearby storefronts.

Earlier Thursday, a car bomb was detonated as an Iraqi police patrol passed in a volatile area of central Baghdad, killing four people, including two policemen, and wounding 11, according to police.

Gunmen also opened fire on a police patrol near the al-Shaab stadium in eastern Baghdad, killing one policeman and wounding another, police said.

Nobody claimed responsibility for the attacks, but car bombings are the hallmark of Sunni militants, who appear to be taking advantage of a waiting period before a planned U.S.-Iraqi security crackdown in Baghdad to step up attacks on Shiites.

There had been a relative lull in Baghdad violence since the first of the year, although dozens of bodies have turned up daily after being dumped on the streets, apparent victims of so-called death squads largely run by Shiite militias.

The bombings and shootings came a day after a suicide car bomber killed 17 Shiites at a teeming Sadr City market, while gunmen in a predominantly Sunni neighborhood of Baghdad shot up a convoy of democracy workers in an ambush that took the lives of an American woman and three bodyguards.

An Iraqi army officer, who spoke on condition of anonymity because of security concerns, said the attack on the Western convoy took place in Yarmouk, a predominantly Sunni neighborhood in western Baghdad.

The three-car convoy belonged to the Washington-based National Democratic Institute, according to Les Campbell, the not-for-profit group's Middle East director. He said the four dead included an American woman along with three security contractors — a Hungarian, a Croatian and an Iraqi. Two others were wounded, one seriously, Campbell said by telephone from Washington. Their names were withheld until their families could be notified.

"It appeared to be an attack with fairly heavy weapons, we don't know what kind," Campbell said. "We have some information that a firefight ensued. Our security company responded to the attack."

Campbell said the ambush took place at midday as the group returned from a program elsewhere in Baghdad.

Click here for FOXNews.com's World page.