The military said the crash occurred about 2:15 a.m. and that it did "not appear to be by enemy action." No precise location was given.
Iraqi officials said the crash site was located about 20 miles (30 kilometers) west of Kirkuk, which is about 180 miles (290 kilometers) north of Baghdad. They spoke on condition of anonymity because they were not supposed to release the information.
Maj. Derrick Cheng, a spokesman for U.S. forces in northern Iraq, said all the dead were Americans.
The deaths raised to at least 4,236 members of the U.S. military who have died in the Iraq war since it began in March 2003, according to an Associated Press count.