The Kosovo government postponed implementation of a decision that would oblige Serbs in the north of the country to apply for car license plates issued by Pristina institutions after tensions rose between police and local communities that set roadblocks.
Late on Sunday the protesters parked trucks filled with gravel and other heavy machinery on the roads leading to the two border crossings, Jarinje and Bernjak, in a territory where Serbs form a majority. Kosovo police said they had to close the border crossings.
"The overall security situation in the Northern municipalities of Kosovo is tense," NATO-led mission to Kosovo KFOR said in a statement.
In Moscow, Russian Foreign Ministry spokeswoman Maria Zakharova blamed the heightened tension on what she called "groundless discriminatory rules" imposed by Kosovo authorities
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 recognize institutions under the capital, Pristina. Kosovo has been recognized as an independent state by more than 100 countries but not by Serbia or Russia.
The government of Prime Minister Albin Kurti said it would give Serbs a transitional period of 60 days to get Kosovo license plates, a year after giving up trying to impose them because of similar protests.
The government also decided that as of August 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.
But following tensions on Sunday evening and consultations with EU and U.S. ambassadors, the government said it would delay its plan for one month and start the implementation on September 1.
Earlier on Sunday, 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.
Air raid sirens were heard for more than three hours in the small town of North Mitrovica inhabited mainly by Serbs.
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 remain high, and Kosovo's fragile peace is maintained by a NATO mission that 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 dialog sponsored by the European Union to try to resolve outstanding issues but little progress has been made.