Dozens of ethnic Albanians have gathered in Kosovo's northern city of Mitrovica to demonstrate against rising tensions in the Balkan nation.

At least 100 Albanians gathered on Thursday on the main bridge over the Ibre River that separates the Albanian and Serb-populated parts of the city, where security has been increased by the Kosovo police and NATO's Peacekeeping Force in Kosovo (KFOR) units.

They unfurled Kosovo and Albanian flags, and chanted slogans in favour of the Kosovo Liberation Army (UCK) and against Serbia.

Unrest in Kosovo's north has intensified since ethnic Albanian mayors took office in the region's Serb-majority area. The majority Serb population had boycotted the April election, allowing ethnic Albanians to win the poll despite a turnout of less than 3.5 percent.

Serbs have been protesting outside these municipalities since Monday when the mayors took their oaths and began their official duties.

Thirty peacekeepers and 52 Serbs who protested against the elections were injured in violence on Monday.

The clashes prompted NATO to announce it would send additional troops on top of 700 already on their way to the Balkan country to boost its 4,000 strong mission.

US, France and Germany intensify diplomatic pressure

Kosovo Prime Minister Albin Kurti has said he will not back down from the decision to appoint the mayors.

"Mayors should go and work in their offices," Kurti told Kosovo Albanian media. "We need to have normality... What is the meaning of having public buildings for state officials if they are not used?"

US Secretary of State Antony Blinken urged both Pristina and Belgrade to ease tensions, warning they were putting aspirations of European integration at risk.

French president Emmanuel Macron said France and Germany urged the leaders of Kosovo and Serbia to organise new elections as soon as possible. Speaking at a political summit in Moldova, Macron added that France and Germany had also asked for Kosovo's election rules to be clarified.

Macron and German Chancellor Olaf Scholz are expected to meet Kosovo President Vjosa Osmani and her Serbian counterpart Aleksandar Vucic on the sidelines of the summit.

Vucic said he talked with EU foreign policy chief Josep Borrell about "irresponsible behaviour of Pristina institutions", adding that Kosovo representatives did not want to meet with Serbian leaders during the summit.

Kosovo declared independence from Serbia in 2008. But Belgrade, along with China and Russia, still does not recognise the move, preventing Kosovo from having a seat at the United Nations.