Kosovo and Serbia must de-escalate a tense situation in the region, the European Union's foreign policy chief has said, after Serb protesters in northern Kosovo blocked main roads for a third day.

In recent weeks Serbs in northern Kosovo have responded with violent resistance to moves by the Kosovan government that they see as anti-Serb.

"I know the two parts are willing to de-escalate and I strongly call on the two of them to do it," Mr Borrell said as he arrived at a meeting of EU foreign ministers.

"They have to comeback to the dialogue, they have to overcome this tendency to fighting in the street."

The latest protests were triggered by the arrest of a former police officer on Saturday.

He was part of a mass resignation of Serbs from the force last month, after the Kosovan government said it would require Serbs to scrap Serbian licence plates dating to before the 1998-99 Kosovo War that led to independence.

Trucks and other heavy-duty vehicles blocked several main roads leading to two border crossings with Serbia this morning. Both crossings were closed to traffic.

Polish troops, part of the NATO peacekeeping mission, were monitoring one of the six road blocks where trucks filled with gravel were parked in the village of Rudare close to the town of Mitrovica.

In the ethnically mixed area, police carrying automatic rifles were patrolling and guarding an election office where last week Serb protesters attacked police and smashed some of the building's windows.

Kosovo had planned to hold local elections next Sunday in four municipalities after their mayors quit, but President Vjosa Osmani postponed the votes until April citing security concerns.

EULEX, the European Union mission tasked with patrolling northern Kosovo, said a stun grenade was thrown at one of its armoured vehicles on Saturday evening, but no one was injured.

Russia calls for diplomatic solution

The Russian government has also called for a "diplomatic" resolution to the recent flare-up in tensions.

"We are in favour of the parties making efforts of a peaceful nature and this situation being resolved through diplomatic means," Kremlin spokesman Dmitry Peskov said.

"We stand for ensuring that all the rights of the Serbs are guaranteed," he added.

With historically close ties, Serbia is one of Russia's few remaining allies in Europe after President Vladimir Putin ordered troops into Ukraine.

Although Kosovo declared independence from Serbia in 2008, Belgrade does not recognise it and encourages the Serb majority in northern Kosovo to defy Kosovan authority.