PHNOM PENH, CAMBODIA, JULY 25 -- A mass grave from Khmer Rouge "killing fields" 10 miles southwest of here has yielded four sets of human remains that a visiting U.S. technical team said "show a possibility of being American."

After an honor-guard ceremony at Phnom Penh's airport, six sets of remains will be flown to Hawaii for further examination. In addition to the four from the mass grave, two other sets found in border areas were accepted for testing.

This was the first official U.S. mission here since 1975 to seek remains of Americans reported missing in action in Cambodia during the Vietnam war. It is also the first official contact between the U.S. and the Vietnamese-backed Cambodian government. Only 83 Americans are counted as missing here, compared to more than 1,000 in Vietnam and 500 in Laos after two decades of U.S. military involvement in the region.

Many of the Americans listed as missing in Cambodia were on planes shot down while on bombing raids or reconnaissance missions.

That four sets of "possibly American" remains were found in a mass grave at Choeung Ek suggests that some Americans -- or other Westerners -- may have been among the hundreds of thousands of Cambodians who fell victim to the Communist Khmer Rouge during its 1975-78 rule.

About 20,000 victims of Khmer Rouge violence were buried at the site. Their bones have since been dug up and displayed in neat pyramids.