PRISTINA, Serbia, Oct 10 (Reuters) - Police in Kosovo were evacuating the main building of the United Nations mission in the province to investigate a suspect device found in a police car, officials said on Wednesday. Kosovo police spokesman Veton Elshani said the device had been found during a routine sweep of a U.N. police car returning to the car park. "We don't know what it is, but they are closing down the compound," a U.N. source said. Police cordoned off the street in front of the building of the mission that has run the breakaway Serbian province since 1999, when NATO expelled Serb forces accused of ethnic cleansing of Albanian civilians while fighting separatist guerrillas. The province's 90-percent Albanian majority is impatient for independence. Frustration has been mounting in recent months at the West's stalled bid to grant them independence in the face of Serbian and Russian opposition. Some in the province have turned against U.N. authorities, blaming them for the political limbo that has kept Kosovo in poverty. In 2005, a bomb exploded in the car park of the U.N. building, destroying several cars and shattering windows.