A group of Marines walk the beach outside the Haleiwa Incident Command Post in Haleiwa, Hawaii, during search efforts for 12 missing Marines, in this handout photo taken January 18, 2016. REUTERS/U.S. Coast Guard/Petty Officer 1st Class Levi Read/Handout via Reuters

(Reuters) - Trace elements of DNA have been discovered from U.S. Marines who died when two helicopters crashed off the coast of Hawaii last month, the Marine Corps said on Tuesday, although no bodies have been found.

The death toll of 12 Marines ranks the incident among the worst training mishaps the U.S. military has suffered during the last decade.

The DNA traces were recovered during search and rescue missions that ended on Jan. 19, and the families of the dead Marines were informed, the Marine Corps said in a statement.

“None of the 12 Marines that were involved in the January 14 mishap have been recovered,” it added.

The Marines, whose ages ranged from 21 to 41, were aboard two CH-53E helicopters on a routine training mission off the island of Oahu at the time of the crash.

The cause of the crash is still being investigated, along with the possibility that the two craft collided, military officials have said.

Recovery and salvage operations can take several months to complete, the Marine Corps said. Storms hampered the search effort over some 40,000 square nautical miles of ocean, as well as shorelines.