Kosovo's biggest border crossing with Serbia was closed on Wednesday as months of tensions again flared, prompting Washington and Brussels to urge an immediate de-escalation of tensions.

Kosovo declared independence from Serbia in 2008, but Belgrade has refused to recognise it and encouraged Kosovo's 120,000 ethnic Serbs to defy Pristina's authority – especially in the north where ethnic Serbs make up the majority.

The latest trouble erupted on December 10, when ethnic Serbs put up barricades to protest the arrest of an ex-policeman suspected of being involved in attacks against ethnic Albanian police officers – effectively sealing off traffic on two border crossings.

After the roadblocks were erected, Kosovar police and international peacekeepers were attacked in several shooting incidents, while the Serbian armed forces were put on heightened alert this week.

Late Tuesday, dozens of demonstrators on the Serbian side of the border used trucks and tractors to halt traffic leading to Merdare, the biggest crossing between the neighbours – a move which forced Kosovo police to close the entry point on Wednesday.

"Such an illegal blockade has prevented the free movement and circulation of people and goods, therefore we invite our citizens and compatriots to use other border points for circulation," a Kosovo police statement said.

Pristina also asked NATO-led peacekeepers to clear the barricades that were erected on Kosovo soil.

Meanwhile, the European Union and the United States voiced concern over the situation and urged its immediate de-escalation.

"We call on everyone to exercise maximum restraint, to take immediate action to unconditionally de-escalate the situation, and to refrain from provocations, threats, or intimidation," they said in a joint statement.

The EU and US said they were working with Serbian President Aleksandar Vucic and Kosovo's Prime Minister Albin Kurti to seek a political solution to one of the worst flare-ups in years in northern Kosovo.

Earlier on Wednesday, Serbian Defence Minister Milos Vucevic said that Belgrade was "ready for a deal", but did not elaborate.

Vucevic described the roadblocks as a "democratic and peaceful" means of protest and added that Serbia has "an open line of communication" with Western diplomats on resolving the issue.

"We are all worried about the situation and where all this is going... Serbia is ready for a deal," Vucevic told the state-controlled public broadcaster RTS. (AFP)