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DUBAI, May 13 (Reuters) - The self-styled Islamic State in Iraq, an al Qaeda-led group, said on Sunday it was holding "crusader" soldiers after a clash with their patrol on Saturday.

U.S. troops backed by helicopters have been searching for three American soldiers who went missing in an al Qaeda stronghold near Baghdad on Saturday after an ambush that killed four other U.S. soldiers and an Iraqi army interpreter.

"God has enabled your brothers at the Islamic State in Iraq on Saturday ... to clash with a crusader patrol in Mahmudiya area at the southern part of Baghdad," its said in a statement posted on a Web site used by insurgent group.

"Some were detained and some were killed," it said without giving numbers. "We will provide the full details of this blessed operation as soon as they are available," it added.

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