BAGHDAD, Jan 18 (Agencies): A suicide car bomber killed 17 Shiites at a teeming Sadr City market Wednesday, 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.
The attack on the marketplace came one day after car bombings killed scores of university students just two miles away, indicating that al-Qaida-linked fighters are bent on a surge of bloodshed as U.S.
and Iraqi forces gear up for a fresh neighborhood-by-neighborhood security sweep through the capital.
Although nobody claimed responsibility for either day's car bombings, such attacks are the hallmark of Sunni militants, who appear to be taking advantage of a waiting period before the security crackdown to step up attacks on Shiites.
There had been a relative lull in Baghdad violence since the first of the year.
Prime Minister Nouri al-Maliki said Wednesday that 400 militiamen loyal to radical Shiite cleric Muqtada al-Sadr had been arrested "within the last few days," the New York Times reported on its Web site.
It was the first time al-Maliki claimed significant action against the militia, the Mahdi Army, which has been blamed for much of the sectarian killings in the past months.
A senior government official later told the New York Times that the total number arrested was 420, including several dozen senior leaders detained in the past several weeks.
The senior official spoke to the newspaper on condition of anonymity.
State television also reported that at least 100 insurgents were killed Wednesday in clashes with Iraqi troops in a predominantly Sunni region northeast of Baghdad.
Troops captured dozens of insurgents and seized large amounts of ammunition, the state-run Iraqiya channel said, quoting police.
The fighting reportedly took place near the district of Balad Ruz, 45 miles northeast of the capital.
The report couldn't immediately be confirmed with Iraqi authorities.
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.