The US military statement says all seven people aboard a Marine Sea Knight helicopter were killed when it crashed Wednesday in Iraq.
Major General William Caldwell says the helicopter went down in Anbar province, about 20 miles northwest of Baghdad. He says the crash is under investigation.
A senior US defense official says the mechanical problems are suspected, not hostile fire.
Earlier, Sunni insurgents linked to al-Qaida claimed to have brought down the C-H-46 helicopter, and an Iraqi air force official said an anti-aircraft missile was to blame.
It's the fifth American helicopter to go down in Iraq in just over two weeks.
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