The NATO-led KFOR peacekeeping force on Monday said that 25 of its troops were injured in the clashes with ethnic Serbs in northern Kosovo who were trying to take over the offices of one of the municipalities where ethnic Albanian mayors took up their posts last week. Serbs began clashing with the police in the morning in the municipality of Zvecan, 45 kilometers (28 miles) north of the capital Pristina. In the afternoon, KFOR soldiers called on Serbs to clear the way for two vehicles from the Kosovar special police forces. The soldiers then used tear gas and stun grenades to protect the Kosovar officers in the vehicles and disperse protesters, according to witnesses and local media. The assembled Serbs responded by throwing rocks and other hard objects. Some Kosovo police vehicles and one belonging to journalists were damaged. Pictures showed graffiti with Serb nationalist symbols sprayed over them. Earlier, journalists were sent into the public building for their own safety. The violence was the latest incident as tensions soared over the past week, with Serbia putting the country's military on high alert and sending more troops to the border with Kosovo, which declared independence from Belgrade in 2008. Kosovo and Serbia have been foes for decades, with Belgrade refusing to recognise Kosovo's sovereignty. The United States and the European Union have stepped up efforts to help solve the Kosovo-Serbia dispute, fearing further instability in Europe as Russia's war rages in Ukraine. The EU has made it clear to both Serbia and Kosovo they must normalise relations if they are to make any progress toward joining the bloc. Speaking in Zvecan, the U.S. ambassador to Kosovo said he had met with Prime Minister Albin Kurti to try and find a way to calm tensions. "There is agreement that de-escalation needs to happen but I don’t know that I can say it's agreement on how it would happen," Jeff Hovenier said. One proposal put forward by the U.S. is for the newly elected ethnic Albanian officials to not work from the municipal buildings, Hovenier told journalists. "Just as the government was able to find the way for them to receive their oaths in other alternative buildings to avoid the conflict and the perception of increased intentions over that, we also think that's the appropriate way right now for them to work," he said. Also Monday, Kosovar police and KFOR were seen protecting the municipal buildings in Leposavic, Zubin Potok and Mitrovica, in addition to Zvecan - four communes in the north that held early elections last month. The votes were largely boycotted by ethnic Serbs, who form the majority in those areas. Only ethnic Albanian or other smaller minority representatives were elected to the mayoral posts and assemblies. Police said that Serbs gathered early in the morning at three of the municipal buildings — in Zvecan, Leposavic and Zubin Potok but not in northern Mitrovica. In Zvecan, they tried to enter using violence and tear gas. Police responded with tear gas spray, a statement said. Serbs say they want both the new mayors, whom they called “illegal and illegitimate sheriffs,” to resign and leave the offices, and special police to leave northern Kosovo, according to Goran Rakic, a local Serb politician. KFOR said it had increased its presence in the four municipalities, including Mitrovica. It called on all sides to refrain from actions that could cause escalation and urged both “Belgrade and Pristina to engage in the EU-led dialogue.” The conflict in Kosovo erupted in 1998 when separatist ethnic Albanians rebelled against Serbia’s rule, and Serbia responded with a brutal crackdown. About 13,000 people, mostly ethnic Albanians, died. NATO’s military intervention in 1999 eventually forced Serbia to pull out of the territory. Washington and most EU countries have recognised Kosovo as an independent state, but Serbia, Russia and China haven't.