Serbs in northern Kosovo have erected new barricades in the ethnically divided city of Mitrovica using trucks loaded with rocks.
The latest flare-up in tensions was triggered by the arrest of a Serb former police officer in early December.
Some 50,000 Serbs live in the northern part of the country in which ethnic Albanians make up the majority of the population.
Local Serbs refuse to recognise the Pristina government and see Belgrade as their capital. Kosovo declared independence from Serbia in 2008.
Serbia troops on highest alert
The latest barricades were erected hours after Belgrade said it had put its army on the highest combat alert following weeks of escalating tensions between the two countries.
Serbian President Aleksandar Vucic said he had ordered the move as he believed Kosovo was preparing to attack Serbs and forcefully remove the barricades they started putting up 18 days ago to protest the policeman’s arrest.
Meanwhile, Serbia's defence minister, Milos Vucevic, has carried out an inspection of troops near the Kosovo border.
And Pristina has asked the NATO-led peacekeepers stationed in the region to remove all the barricades, hinting that it might otherwise remove them by force.
Some 4,000 peacekeepers have been stationed in Kosovo since the 1999 war that ended with Belgrade losing control over the territory.
Attempts to reach a negotiated settlement between the two countries have failed, with Serbia refusing to recognise Kosovo’s statehood.
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