Serbs from Kosovo's north earlier on Saturday blocked main roads in the region to protest against the arrest of a former member of the Kosovo police who quit his post last month along with other ethnic Serbs.Serb mayors in northern Kosovo municipalities, along with local judges and some 600 police officers, resigned last month in protest over a government decision to replace Belgrade-issued car licence plates with ones issued by Pristina.Belgrade bears the full responsibility for any escalation," Blerim Vela, Kosovo's presidential chief of staff, said on Twitter.On Thursday, a policeman was injured in an attack on a patrol after police ranks in the area had been reinforced by non-Serb officers following the mass resignations.In an urgent press conference, Serbia's President Aleksandar Vucic said he would ask NATO's KFOR peacekeeper mission to let Serbia deploy troops and police in Kosovo, although he acknowledged there was no chance of permission being granted."