The thousands of U.S. troops searching for three missing comrades in Iraq are being slowed by buried bombs, it was reported Sunday. The bombs are meant to explode as troops fan out on foot in search of the soldiers, missing since a May 12 attack on their patrol, UPI reported. "They're putting them in places where we're more likely to be dismounted," said Lt. Col. Robert Morschauser. "We've seen it before. But they're using more of it." At least four of the bombs have hit foot patrols in the Sunni stronghold south of Baghdad where the men were captured, the New York Times reported Sunday. The only two American soldiers known to have been killed during the search died after stepping on or near bombs. The bombs have added new fears to the urgent effort by 4,000 U.S. soldiers and 2,000 Iraqi soldiers, working long days with little rest to track leads across wide stretches of rural land, the Times said.