NATO's forces in Kosovo announced they are ready to intervene if stability in northern Kosovo is threatened.
NATO's forces in Kosovo are prepared to intervene if stability is endangered in the north of Kosovo, KFOR said in a press release.
Tensions between Pristina and Belgrade are running high as air raid sirens were heard for more than three hours in the small border town of Mitrovica.
"The NATO-led KFOR mission is monitoring closely and is prepared to intervene if stability is jeopardised, in accordance with its mandate, coming from UNSC Resolution 1244 of 1999," the statement said on late Sunday.
The commander of KFOR is in contact with all of his main interlocutors, Serbian and Kosovar senior defence officials to calm the tensions, the statement said.
"KFOR will take whatever measures are necessary to keep a safe and secure environment in Kosovo at all times, in line with its UN mandate," it added.
Fourteen years after Kosovo declared independence from Serbia, some 50,000 Serbs living in the north use license plates and documents issued by Serbian authorities, refusing to recognise institutions under the capital, Pristina.
Kosovo has been recognised as an independent state by more than 100 countries but not by Serbia or Russia.
Kosovo police said they closed two border crossings in the volatile north after local Serbs blocked roads and fired shots at police in protest at an order to switch Serb car license plates to Kosovar ones within two months.
The government of Prime Minister Albin Kurti said it would give Serbs a transitional period of 60 days starting Aug 1 to get Kosovo license plates, a year after giving up trying to impose them due to similar protests.
The government also decided that as of Aug 1, all citizens from Serbia visiting Kosovo would have to get an extra document at the border to grant them permission to enter.
A similar rule is applied by Belgrade authorities to Kosovars who visit Serbia.
The protesters parked trucks filled with gravel and other heavy machinery on roads leading to the two border crossings, Jarinje and Bernjak, in a territory where Serbs form a majority.
As a consequence, Kosovo police said they had to close the border crossings. “We call on all citizens to use other border crossings,” the police said on their Facebook page.
Police said there were shots fired "in the direction of police units but fortunately no one was wounded".
It also said angry protesters beat up several Albanians passing on the roads that had been blocked and that some cars had been attacked.
A year ago, after local Serbs blocked the same roads over license plates, Kosovo’s government deployed special police forces and Belgrade flew fighter jets close to the border.
Tensions between the two countries are now at their highest in years and Kosovo’s fragile peace is maintained by a NATO mission which has 3,770 troops on the ground. Italian peacekeepers were visible in and around Mitrovica on Sunday.
The two countries committed in 2013 to a dialogue sponsored by the European Union to try to resolve outstanding issues but little progress has been made.
Kosovo, which is predominantly inhabited by Albanians, broke away from Serbia in 1999 and declared its independence in 2008. It is recognized by more than 100 countries, including the US, UK, France, Germany, and Türkiye. Serbia has not recognized this and continues to lay claim to the territory.