Baghdad, Iraq ? Some 1,600 U.S. and Iraqi soldiers pushed into a dangerous Sunni Arab area of west Baghdad on Wednesday, searching houses in the expanding security crackdown, while at least 33 apparent victims of sectarian killings were found dumped across the capital.

A woman leads her children past U.S. army soldiers from the 1st Battalion, 23rd Infantry Regiment on Wednesday in western Baghdad's Sunni neighborhood of Ghazaliyah, Iraq. U.S. troops conducted a major house search in parts of Ghazaliyah Wednesday.

The U.S. military said the armor-backed force that swept into the Ghazaliyah and Amariyah neighborhoods detained 31 people and found two weapons caches that included containers of nitric acid and chlorine, a toxic material used recently by Sunni insurgents in bomb attacks.

No casualties were reported during the first day of the operation, which included about 1,100 American soldiers and 500 Iraqi troops.

The move was certain to ease tensions with Shiite Muslims in districts to the east. They had complained bitterly of being hit by mortar shells that Sunni fighters fired from Ghazaliyah at will.

Police, meanwhile, said children had been used as decoys in a weekend car bombing in which the driver gained permission to park in a busy Shiite shopping area after he pointed out he was leaving his children in the back seat.

The bomb was exploded with the children still in the car, police said, perhaps signaling a new tactic by insurgents who are seeking to foment all-out civil war between Shiites and Sunnis.

A police commander in north Baghdad’s Shaab neighborhood speculated the youngsters were kidnap victims. He and other police officers who reported the incident spoke on condition of anonymity, saying they were not authorized to release the information to reporters.

The accounts appeared to confirm one given Tuesday in Washington by Maj. Gen. Michael Barbero, deputy director for regional operations on the Joint Staff.

Barbero said a car used in a Sunday bombing had been waved through a U.S. checkpoint because soldiers saw youngsters in the back. He called it a brutal tactic by insurgents seeking to battle the security crackdown in Baghdad.