The U.S. Defense Department on Sunday identified three U.S. Army trainers killed on Friday when their convoy came under fire as it entered a military base in Jordan.

The Pentagon said the three were members part of an Army Special Forces Group based at Fort Campbell, Kentucky.

In a statement, it identified the dead soldiers as Staff Sergeants Matthew C. Lewellen, 27, of Lawrence, Kansas; Kevin J. McEnroe, 30, of Tucson, Arizona; and James F. Moriarty, 27, of Kerrville, Texas.

Details of the deadly incident - unusual given the close political and military ties between Washington and Amman - remain under investigation.

A Jordanian military source told Reuters the U.S. trainers were fired on by Jordanian security forces when they failed to stop at the gate of Prince Faisal air base in the south of the country.

Other Jordanian sources, however, said they could not rule out political motives in the incident.