A man who claimed in a widely publicised documentary to be an American soldier, missing since his helicopter was shot down during the Vietnam War, is actually Vietnamese, the US said. "Unclaimed", directed by Michael Jorgensen, which has generated an explosion of interest since its premiere this week, purports to have discovered US serviceman John H. Robertson -- alive, well and living in the communist nation. But a United States Defense Department statement said the man -- who appeared on film in an emotional "reunion" with Robertson's sister -- has been DNA tested and found to be a citizen of the Southeast Asian country. "All claims and alleged live sighting reports related to Robertson have been investigated and found to be false," according to a release from the Defense Prisoner of War/Missing Personnel Office on Thursday, provided to AFP by the US Embassy in Hanoi. A tightly edited trailer for the movie, posted on production company Myth Merchant Films' website, does not show any clear full-face images of the Vietnamese man, known by the name Dang Ngoc Than. Nearly 60,000 American soldiers died in the bloody Cold War-era conflict, which also claimed the lives of up to three million Vietnamese civilians and soldiers before ending in 1975 with Vietnam's reunification. Robertson was on board a Vietnamese Air Force H-34 helicopter that came under heavy enemy ground fire in May 1968 and crashed, leaving no survivors. He was declared dead in 1976. The documentary shows Robertson's elderly sister in an emotional reunion with the man claiming to be her brother. The film-makers in a post on their Facebook page said the movie was not "produced to help perpetrate fraud of any kind or misrepresent anyone's identity". Investigators interviewed the Vietnamese man twice, in 2004 and 2009, after "alleged live sighting reports", according to the US statement. Fingerprint samples taken at the time were not the same as those on file for the missing serviceman, it said, and DNA "did not match either of Robertson's siblings". "A recently released film features this same Vietnamese individual who continues to allege that he is Robertson," the statement added. Had the man been proven to be Robertson, he would theoretically have been entitled to back pay and veterans' benefits from the US government. When the guns fell silent, 1,971 Americans were left unaccounted for, according to figures from the US Joint Prisoners of War, Missing in Action Accounting Command (JPAC), which handles the search for MIAs.