PRISTINA, Dec 22 (Reuters) - (This Dec. 22 story has been corrected to say that police officers were transported by NATO via ground routes, not by helicopter, in paragraph 7)Kosovo has asked NATO troops to airlift a former Serb policeman who was detained two weeks ago but could not be transferred elsewhere because local Serbs demanding his release set up barricades to prevent him being moved.Tensions have been running high since then as thousands of Kosovo Serbs protest, demanding the country's Albanian-majority government pulls its police force out of the north, where the Serb minority is concentrated."He (Pantic) should be in a detention center and not in a police station and that's why we have asked our international partners to transfer him in an adequate facility," Interior Minister Xhelal Svecla told a news conference in Mitrovica, just a few kilometers away from the first barricade.KFOR has already transported via ground routes nine police officers in recent days who were ill but unable to get out of the area after the roads were blocked.Ethnic Serb mayors in northern municipalities, along with local judges and some 600 police officers, resigned last month in protest over a Kosovo government decision to replace Serbian-issued car license plates with ones issued by Pristina."