Witnesses described the helicopter weaving in air before it plowed into a mountainside in central Vietnam on Saturday.
"I heard the helicopter flying very low. The engine made a big noise, and then we heard a big explosion. It was very foggy so we couldn't see very much," said Nguyen Van Minh, 45.
"It was like during the Vietnam War again when we ran to see if we could help anyone from the crash. There was only one man who was still alive. He told us he was with the MIA team," he said. That man, a Vietnamese, died shortly afterward.
Those killed were the advance team for a 95-member Hawaii-based American group that was scheduled to begin work at six MIA recovery sites in Vietnam in early May, said Army Lt. Col. Franklin Childress, spokesman for the MIA task force.
The bodies were carried down on stretchers from the mountain in Bo Trach district in Quang Binh province, about 280 miles south of Hanoi.
The identities of the victims were not released pending notification of their families. Their bodies were driven in ambulances to Hanoi, and the Americans were to be repatriated to Hawaii later this week.
Among those believed to be on board were the commanding officer of the MIA team in Hanoi, as well as the deputy commanding officer and the incoming head of the Hanoi team.
Officials were investigating the cause of the accident. A local official said the team had called earlier Saturday to say they were canceling a stop in Dong Hoi, the capital of Quang Binh province, because of bad weather.
The helicopter - a chartered Vietnamese military aircraft - was on its way to the town of Hue instead when it smashed into the mountain. A tattered rotor blade jutting from the hillside served as a grim marker over a valley of emerald-green rice paddies.
Local police secured the area and confiscated the camera of an Associated Press photographer. Curious villagers watched from the valley as officials recovered wreckage from the mountain.
Childress said no decision has been made whether the MIA mission would go on. U.S. Defense Secretary Donald Rumsfeld said the overall program of accounting for MIAs and recovering their remains will continue.
"We've been flying in this type of helicopter for a number of years, and this is the first accident," Childress said in Hawaii. "Every mission is a dangerous mission. It's a very difficult area to operate in."
Vietnam's Foreign Ministry called the accident "a huge loss to Vietnam as well as to the United States" and sent condolences to the U.S. government, people and families of the victims.
The Joint Task Force-Full Accounting, based in Camp H.M. Smith, Hawaii, has searched for MIA remains from the Indochina War in Vietnam, Laos, Cambodia and southern Cina since 1992, and in recent years has expanded operations to include World War II and Korean War MIA recovery cases.
The United States spends up to $6 million each year conducting regular searches, which often involve helicopter flights carrying both U.S. and Vietnamese military personnel and civilians into remote areas.
Since 1973, the remains of 591 American service members formerly listed as unaccounted for have been identified and returned to their families. There are 1,992 Americans still unaccounted for from the war in Southeast Asia, including 1,498 in Vietnam.
Quang Binh province was the southernmost province of North Vietnam during the war, just north of the former demilitarized zone. It contains many military crash sites because it was heavily bombed during the war.
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