Kosovo police said they closed two border crossings in the volatile north after local Serbs blocked roads and fired shots at police in protest against an order to switch Serb car license plates to the ones issued by Kosovo within two months.

Fourteen years after Kosovo declared independence from Serbia, some 50,000 Serbs living in the north still use license plates and documents issued by Serbian authorities, refusing to recognize institutions under Kosovo.

Kosovo 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 due to similar protests.

It also decided that as of August 1, all citizens from Serbia visiting Kosovo would have to get an additional document at the border to grant them entry.

Belgrade authorities have a similar rule for Kosovo people who visit Serbia.

But following tensions on Sunday evening and consultations with EU and U.S. envoys, Kosovo said it would delay its plan for one month and start implementation on September 1, a move welcomed by the European Union's foreign policy chief Josep Borrell.

"Expect all roadblocks to be removed immediately," Borrell said in a tweet.

Earlier on Sunday, police said shots were 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 deployed special police forces, and Belgrade flew fighter jets close to the border.

Tensions between the two neighbors 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.

In 2013, Serbia and Kosovo committed to a dialogue sponsored by the European Union to try to resolve outstanding issues, but little progress has been made.

(With input from Reuters)