Two sets of possible American remains, including one believed linked to the unsolved sinking of a landing craft during the Vietnam War, were returned home on Wednesday, US officials said.
The repatriation from Da Nang, in central Vietnam, was mounted after the latest mission to locate Americans listed as missing in action from the war which ended almost four decades ago.
A total of 11 US soldiers were lost when the landing craft, used to transport supplies along the coast, sank in 1970, said Ron Ward of the Joint POW/MIA Accounting Command (JPAC).
"We don't know if they got hit by a rogue wave or something. It went down and nobody really knows why," he said.
Possible remains of at least one of the missing soldiers were found near the shore off Thua Thien-Hue province during JPAC's just-concluded investigation and excavation mission, he said.
Further north in Quang Tri province, JPAC investigators working with their Vietnamese counterparts recovered the suspected remains of a soldier killed by an explosion in a bunker in 1968, Ward said.
"We brought an American veteran... to help us find that site," he added.
A JPAC lab in Hawaii will examine the repatriated material.
Wartime enemies the US and Vietnam began cooperating on investigations into missing American servicemen in 1985, helping pave the way for a normalization of diplomatic relations 10 years later.
Since the end of US combat involvement in 1973, the remains of more than 660 Americans listed as missing during the war have been repatriated from Vietnam and identified, but 1,296 are still unaccounted for, the US says.
About 300,000 Vietnamese soldiers of the liberation forces are still listed as missing from the war, according to Hanoi.