BAGHDAD &

Attackers who ambushed a U.S. military convoy apparently stole the dog tags of one of the four American soldiers killed, the military said today as it pressed its massive search for three U.S. troops feared captured by al-Qaida last week.




Mortar rounds hit a U.S. Air Force base north of Baghdad, destroying one helicopter and damaging nine others, police said, and an explosion rocked the Green Zone in the third attack in three days on the heavily fortified area in central Baghdad where the U.S. Embassy is located and Iraq's government and parliament meets.




No casualties were immediately reported in either of those attacks.




Maj. Webster Wright, a spokesman for the Second Brigade of the 10th Mountain Division &

the unit that was attacked and that is leading the search for the three missing soldiers &

said Saturday's assault in an insurgent stronghold south of Baghdad apparently used rocket-propelled grenades and small arms fire to severely damage the two Humvees in the stationary U.S. convoy.




The dog tags of one of the four American soldiers who died were missing and apparently had been taken by the attackers, he said. That could explain why the military has only been able to identify three of the four dead soldiers. The military has said some of the bodies were burned.




About 4,000 U.S. troops and 2,000 Iraqis are searching for the three soldiers feared captured by al-Qaida during the ambush, which also killed one Iraqi soldier.




Maj. Gen. Rick Lynch, commander of U.S. troops south of Baghdad, said the U.S. was offering rewards of up to $200,000 for information on the missing soldiers.




"We've done so much as to drain canals after a report that the bodies were in a canal," Lynch told The Associated Press. "So we're leaving no stone unturned."




Lynch said he was optimistic the three would be found alive, and the search remained focused on the area where they went missing in a rural area near the town of Youssifiyah, 12 miles south of Baghdad.




Wright said a Sunni tribe dominates the area, where many former intelligence agents, Baathists and Republican Guards from Saddam Hussein's government live.




An al-Qaida front group, the Islamic State of Iraq, has said it captured the U.S. soldiers and warned the Americans in a Web statement on Monday to call off the hunt "if you want their safety."




Meanwhile, attacks by suspected insurgents continued in other parts of Iraq.




Mortar rounds hit the Taji U.S. Air Force base on the outskirts of northern Baghdad about 2 a.m., destroying one helicopter and damaging nine others, police said.




An Iraqi civilian who works at the base said he saw about 16 damaged helicopters, some of them set on fire by the mortar attack. The worker spoke on condition of anonymity because he was not authorized to speak to the media.




"There was an indirect fire attack on the base at Taji which resulted in damage to some aircraft," the military said. Indirect fire is a term the military generally uses to describe rocket or mortar attacks.




In Baghdad's Green Zone, one explosion occurred about 2:15 p.m., and U.S. forces were trying to determine whether it was a mortar or a rocket attack, said U.S. Embassy spokesman Lou Fintor. He had no immediate information on casualties.




On Wednesday, about a dozen mortar rounds hammered the sprawling complex , killing at least two Iraqis, wounding about 10 other people and raising new fears for the safety of workers at the nerve center of the American mission in Iraq.




Fintor said at least one explosion occurred in the Green Zone and U.S. forces were trying to determine whether it was a mortar or a rocket attack. He had no information on casualties.




That came a day after about a dozen mortar rounds hammered the sprawling complex, killing at least two Iraqis, wounding about 10 other people and raising new fears for the safety of workers at the nerve center of the American mission in Iraq.




Terrified pedestrians raced for the safety of concrete bunkers. Motorists abandoned their cars and sprinted for cover. Sirens wailed and loudspeakers warned people to seek safety.




Nine people also were wounded in a rocket strike on the 3.5-square-mile area Tuesday, but no U.S. casualties were reported in either attack.




For the second time in a week, a bomb also struck a bridge in southeastern Baghdad on Thursday, killing two civilians and wounding five, police said.




On May 11, a large fuel truck barreled toward a checkpoint at the new Diyala Bridge and blew up, killing about a dozen people, police said.




The bridge, which crosses the Diyala River, a Tigris tributary, also was damaged, and the attack set fire to police and civilian cars driving across it.




Since then, the bridge has been closed to traffic, and Iraqis have been walking across it toward central Baghdad, many to board buses and continue their travels.




Attackers also blew up a bridge that connects an area west of the northern city of Mosul with the autonomous Kurdish region late Wednesday, causing it to collapse, but no injuries were reported, police said.




A roadside bomb exploded Thursday morning near the entrance to the bridge, killing at least two Iraqi pedestrians and wounding five, police said.




At about the same time, an Iraqi police officer was killed in Hillah, about 60 miles south of Baghdad, when a hidden bomb exploded as he left for work, police said. Shrapnel also smashed a window in the house, wounding three of his children, police said.




Insurgents and militias often target Iraqi policemen and soldiers, accusing them of being collaborators with the U.S.-led coalition.




In northern Baghdad, about 200 Iraqis marched in the mostly Shiite neighborhood of Shaab, shouting slogans and carrying banners demanding that the thousands of U.S. soldiers conducting a security crackdown in the capital stop creating forward operating bases in neighborhoods and searching homes for suspected insurgents and militiamen.




In other violence Thursday:




"" Four civilians were killed and four were wounded when fighting broke out in Diwaniyah, 80 miles south of Baghdad, between police and the Madhi Army militia, which is led by the radical cleric Muqtada al-Sadr, police said.




"" A man searching trash for tin cans was killed in the city of Najaf, 100 miles south of Baghdad, when a mortar round left there exploded, police said.




"" A mortar round hit a factory behind a mosque near the Shiite slum of Sadr City in Baghdad, killing one worker and wounding four, police said.




"" The bodies of seven handcuffed and tortured Iraqi men were found, four in Baghdad and three south of the capital, police said. They apparently were the latest victims of death squads that operate in Iraq, motivated by sectarian hatred or the search for ransoms.




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Associated Press photographer Maya Alleruzzo in Baghdad contributed to this report.