BAGHDAD – 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.

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.

The drive to rout Sunni insurgents and Shiite militiamen from strongholds in the capital and surrounding regions is entering its sixth week, and U.S. commanders say they are cautiously optimistic.

The military says that it won’t be able to gauge success on a larger scale until late summer and that many more months are needed to cleanse the center of the country of armed fighters.

An Iraqi official expressed optimism the government is making progress in talks with some insurgent groups, predicting some factions might be close to laying down their arms.

“One of the aims is to join with them in the fight against al-Qaida (in Iraq),” Saad Yousif al-Muttalibi of the Ministry of National Dialogue and Reconciliation told British Broadcasting Corp.

Iraqi police reported that a total of 54 people were killed or found dead across the country Wednesday. Those included at least 41 bodies of apparent sectarian bloodshed, 33 of them in Baghdad and most showing signs of torture.

The number of sectarian murders had dropped sharply in the early days of the security crackdown, falling as low as seven on one day. But such killings have been creeping up again in recent days.

Just north of Baghdad, U.S. troops said they killed five suspected insurgents, detained three others and hit a bomb-making factory with an air strike that destroyed large-caliber ammunition and 50-gallon barrels of explosive material.

The fighting occurred near Taji, 12 miles north of the capital and the site of a large U.S. air base. No American troops or civilians were hurt in the operation, a military statement said.

U.S. troops also increased their numbers in Baghdad’s Hurriyah neighborhood, a volatile Shiite district that saw widespread sectarian attacks on Sunni residents late last year and the deaths of at least three people in a shootout with Iraqi troops Monday.