HONOLULU —  A nuclear submarine that ran aground about 350 miles south of Guam (search), killing one crewman and injuring 23 others, was due back at its home port in Guam on Monday, according to a Navy spokesman.

There were no reports of damage to the USS San Francisco's (search) reactor plant, but the extent of damage to the 360-foot submarine would be determined when it gets to port, said Jon Yoshishige, spokesman for the U.S. Pacific Fleet. The vessel was moving under its own power.

Officials said they still don't know what the Los Angeles-class submarine hit Saturday, but Lt. j.g. Adam Clampitt of the Pacific Fleet (search) said it had been conducting operations underwater at the time.

The incident is under investigation, said Yoshishige.

Navy medical personnel from Guam have been brought aboard the submarine to treat the injuries, which included broken bones, lacerations, bruises and a back injury, the Navy said. The submarine has a crew of 137.

The name of the sailor who died was being withheld pending a mandatory 24-hour waiting period, the Navy said. The sailor's next of kin had been notified.

Located west of the international date line, Guam is a U.S. territory about 3,700 miles southwest of Hawaii.