Serb troops on the Kosovo border were placed on high alert on Friday following clashes inside Kosovo between police and ethnic Serbs that injured more than a dozen people.

Ethnic Serbs from northern Kosovo, who are the majority in that part of the country, had tried to block newly elected ethnic Albanian officials from entering municipal buildings early Friday. Early elections last month were largely boycotted by ethnic Serbs with only representatives of ethnic Albanians or other smaller minorities being elected to mayoral positions and assemblies.

Kosovo police fired tear gas to disperse the crowd and allow the new officials to enter the offices. Several cars were set on fire. Officials at the Kosovo Serb hospital said about 10 protesters were injured. Police said five officers were injured when protesters threw stun grenades and other objects. A police car was burned.

In response to the clashes, Serbian President Aleksandar Vucic said he had put the army on the «highest state of alert» and ordered an «urgent» movement of troops closer to the border. He also demanded that NATO-led troops stationed in Kosovo protect ethnic Serbs from the police.

The United States condemned the Kosovo government for using police to break into municipal buildings.

“These actions have sharply and unnecessarily increased tensions, undermining our efforts to help normalize relations between Kosovo and Serbia and will have consequences for our bilateral relations with Kosovo,” US Secretary of State Antony Blinken said Friday. .

Vucic spoke at a rally Friday night in Belgrade as tens of thousands of people turned out to support the government following two mass shootings earlier this month that killed 18 people and wounded 20 others, shocking the nation.

«We will preserve the peace, but I tell you that Serbia will not sit idly by when the Serbs in northern Kosovo are attacked,» he told the crowd.

Vucic previously warned that Belgrade would respond to violence against Serbs and has stepped up combat readiness several times during times of tension with Kosovo.

However, any attempt by Serbia to send its troops across the border would mean a confrontation with the NATO troops stationed there.

Zdravko Ponos, a former Serbian army chief turned opposition politician, criticized Vucic’s response as «inappropriate.»

“This is just saber rattling to save face for Vucic,” Ponos told regional N1 television.

The Kosovo police acknowledged their increased presence «to help the mayors of the northern communes of Zvecan, Leposavic and Zubin Potok to exercise their right to work.»

The new mayors of three northern communities were prevented from entering municipal buildings, and small groups of Serbs raised their hands at the entrances, apparently to show they were not there to participate in the violence, according to the Albanian news outlet indexonline. .net, which also posted photos

In Zvecan, the news website Kosovo-online.com showed clashes with police in front of the municipal building, while in Leposavic the main square was blocked with cars and trucks.

Local elections were held in four Serb-dominated communes in northern Kosovo after Serb representatives stepped down last year. They had resigned in protest because the Kosovo authorities refused to allow an ethnic Serb association to coordinate work on education, health care, territorial planning and economic development at the local level.

A 2013 Pristina-Belgrade agreement on the formation of the Serb association was later declared unconstitutional by Kosovo’s Constitutional Court, which said the plan did not include other ethnicities and could involve the use of executive powers to impose laws.

The two sides tentatively agreed to back an EU plan on how to proceed, but tensions are still simmering.

The United States and the EU have intensified their efforts to help resolve the dispute between Kosovo and Serbia, fearing further instability in Europe as the war continues in Ukraine. The EU has made it clear to both Serbia and Kosovo that they must normalize relations in order to advance their intentions to join the bloc.

The conflict in Kosovo erupted in 1998 when ethnic Albanian separatists rebelled against the Serbian government, and Serbia responded with a brutal crackdown. Some 13,000 people died, mostly ethnic Albanians. NATO military intervention in 1999 finally forced Serbia to withdraw from the territory. Washington and most EU countries have recognized Kosovo as an independent state, but Serbia, Russia and China have not.