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BAGHDAD, July 4 (Reuters) - A U.S. soldier on board a military helicopter was killed when the aircraft was forced down in northern Iraq on Wednesday, the military said.

A spokesman said it was unclear if the helicopter had taken ground fire, adding the incident was under investigation. He declined to give the type of helicopter or provide more details on the victim.

In a statement, the military said the helicopter came down in Nineveh province.

Another soldier on board had been hurt, the military said. At least 10 helicopters have been shot down in Iraq this year prior to Wednesday's incident, killing 30 people, most of them American military personnel.

An Iraqi al Qaeda-led group said its fighters clashed with U.S. aircraft, including an Apache helicopter whose pilot flew the gunship into a high voltage power cable in an area close to the road between Baghdad and the northern city of Mosul in Nineveh.

"After engaging them with light and medium weapons, God blinded the pilot of one of the aircraft, who collided into a power line ..." the Islamic State in Iraq said in a statement posted on the Internet. (Additional reporting by Inal Ersan in Dubai)

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