Washington's first ambassador to modern Vietnam arrived in Hanoi yesterday hailing a 'new era' in friendship, but insisting the hunt for the remains of US servicemen takes priority. Former prisoner of war Douglas 'Pete' Peterson's opening statements did little to ease the minds of Vietnamese officials and foreign businessmen now desperate for urgent improvements to economic ties and aid flows. 'My mission is to advance United States' interests in Vietnam and our highest national priority is to advance the fullest possible accounting for persons missing from the war,' Mr Peterson said on arrival at Hanoi's Noi Bai airport. 'America and Vietnam have put the conflict behind them, but finding out what happened to the missing is an urgent task for their families and for the nation they honoured. 'I will tell Vietnamese leaders that President Clinton and the American people are grateful for their excellent co-operation in the humanitarian effort.' However, speaking privately, US diplomats were surprised by his remarks and predicted work on a new economic relationship would be the priority. About 100 American residents cheered as Mr Peterson left for the embassy in a white Chevrolet, with the US flag on the bonnet. On-lookers had been asked to fold up flags and banners to obey strict Vietnamese protocol governing the arrival of a foreign envoy. Mr Peterson added that US policy was to help Vietnam prosper and said he had hoped to wrap up a comprehensive trade treaty soon. The deal is crucial to Most Favoured Nation trading status and other federal business advantages but still lacks a formal timetable. Vietnamese officials are confident of agreement by August but US officials have warned there is still much work to be done on the Hanoi side. The exchange of ambassadors completes a thaw in diplomatic ties frozen by the US when communist forces took the former South Vietnam in April 1975. Mr Peterson said he was confident that eventually the two countries would think of each other as good friends rather than former adversaries. 'This is an historical event and the beginning of a new era of constructive relations between our two countries.' Some 1,558 servicemen are still classed as missing in action as a result of the 11-year Vietnam conflict. The $18 million annual hunt for remains involves hundreds of scientists and soldiers in often dangerous conditions. A name can only be removed from the list once identifiable body parts are found. Circumstantial evidence, though considerable in many cases, is not yet acceptable. Mr Peterson spent more than six years inside a string of institutions around northern Vietnam after his jet fighter was shot down near Haiphong in 1966.