"We have conducted more than 450 tactical interviews and detained 11 individuals" as of Monday night, US military spokesman Lt. Col. Christopher Garver said without elaborating.

"We are working with the Iraqi army and the Iraqi police in searching for our missing soldiers. We're also communicating with the local population for information, for support and the local population continues to be helpful in providing tips," Garver said.

Elsewhere, two bombs hidden in plastic bags exploded in shops in central Baghdad, killing at least seven people and wounding 17, and dozens of suspected insurgents attacked a village north of the capital, killing five civilians and wounding 14, Iraqi authorities said.

For a fourth day, jets, helicopters and unmanned surveillance aircraft crisscrossed the skies over the sparsely populated farm area near Mahmoudiya, 20 miles (32 kilometers) south of Baghdad to search for the three missing American soldiers.

US and Iraqi troops _ backed by dog teams _ searched vehicles and pedestrians. Other teams peered into crawl spaces and probed for possible secret chambers in homes.

On Monday, the Islamic State of Iraq _ an al-Qaida front group that has claimed to have captured the soldiers _ warned the US to halt its search by about 4,000 troops, and the Pentagon acknowledged for the first time that it believes the soldiers are in terrorist hands.

Last June, al-Qaida claimed responsibility for the deaths of two US soldiers whose mutilated bodies were later found in the same area where a weekend ambush had occurred.

If all three soldiers now missing are taken hostage alive, it would be the biggest single abduction of US soldiers in Iraq since March 23, 2003, when Pvt. Jessica Lynch and six others were captured in an ambush near Nasiriyah in which 11 Americans were killed.

The three were last seen before a pre-dawn ambush Saturday that destroyed several Humvees in a US convoy and killed four Americans and one Iraqi soldier traveling with them.

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