The helicopter belonged to the Tennessee National Guard and was on a training flight when it crashed at midafternoon near the city of Huntsville, the Tennessee National Guard said in a statement.

The National Guard is a state-based military force that is part of the reserve of the US military when activated for federal missions.

"We are deeply saddened by the loss of two Tennessee National Guardsmen, and our prayers are with their families during this heartbreaking tragedy," Brigadier General Warner Ross, the head of Tennessee's military forces, said in a statement.

It said no other service members or civilians were harmed in the accident.