Baghdad ? Hundreds of American and Iraqi troops backed by helicopters descended Friday on a remote desert area southwest of Baghdad to root out al-Qaida in Iraq and search for two U.S. soldiers missing after a deadly insurgent ambush six months ago.

Acting on intelligence, the soldiers dug with shovels through heaps of sand and went house-to-house after a dramatic predawn air assault into two Sunni villages near the boundary with Anbar province.

U.S. officers said there was no sign of the missing soldiers but stressed it was only the first day of the operation dubbed Marne Courageous, which also aimed to establish a long-term presence west of the Euphrates River in a former al-Qaida stronghold.

Col. Dominic Caraccilo, the commander of the 3rd Brigade Combat Team, 101st Airborne Division, said his troops were taking advantage of anti-al-Qaida sentiment among Sunnis that the military says has played a major part in reducing the violence in Baghdad and surrounding areas.

“The more safe it gets, the easier it is for us to move around and the more we can interact with the populace,” Caraccilo said in a telephone interview. “The more we can interact with the populace, the more they will tell us things.”

The raids began about 4 a.m. after two Chinook helicopters and eight Black Hawks making multiple runs dropped more than 600 U.S. and Iraqi soldiers into the villages of Owesap and Betra, about 15 miles southwest of the Iraqi capital.

Other troops built a 500-foot-long bridge across the river to allow the transport of materials and supplies for a patrol base, which Caraccilo said would take about a month to build.

American F-16 fighter jets dropped two 2,000 pound bombs on an island in the river that was believed to be used by al-Qaida as a staging ground for attacks.

Spc. Alex R. Jimenez of Lawrence, Mass., and Pvt. Byron W. Fouty of Waterford, Mich., were seized May 12 when insurgents attacked and overran a checkpoint in the volatile area south of Baghdad known as the “triangle of death.”

A third soldier, Pfc. Joseph Anzack Jr., was also captured during the raid, but his body was found May 23 floating in the Euphrates River. Four U.S. soldiers and an Iraqi translator were killed during the ambush.

The Islamic State of Iraq, a front group for al-Qaida, claimed in an Internet video that the three missing soldiers were killed and buried. The militants showed images of the military IDs of Jimenez and Fouty but offered no proof that they were dead.