An aide to U.S. Rep. Mary Fallin says three Oklahoma National Guardsmen are among seven soldiers killed in a helicopter crash in southern Iraq.

Fallin's spokesman Alex Weintz says four soldiers from the Texas National Guard also were killed in the crash early Thursday.

The military did not release the names of those killed pending notification of next of kin.

The military says the CH-47 Chinook was flying in a four-helicopter formation to the U.S. military base at Balad, north of Baghdad, when it crashed shortly after midnight.

Military officials say they suspect a mechanical problem was to blame after ruling out hostile fire.

The military says the seven who died were the only people on board.