Ethnic tension ran high in Kosovo after a group of Serb protesters blocked main roads in the northern part of the country for a second day on Sunday.

The blockade comes following a night-time exchange of fire with police after the arrest of a former Serb policeman amid a surge in tensions between the Serb minority and the authorities.

In recent weeks Serbs in northern Kosovo, a hotbed of Serb nationalism, have met attempts by Pristina which they see as anti-Serb with violent resistance.

EULEX, the European Union mission tasked with patrolling the north of Kosovo, said one of the armored vehicle patrols also came under attack from protesters on Saturday evening.

"A stun grenade was thrown at an EULEX reconnaissance patrol last night near Rudare," the EU mission said in a statement. It said no one was injured.

The latest protests were triggered by the arrest of a former police officer Saturday, who was part of an exodus of Serbs from the force last month after Pristina said it would enforce a law requiring Serbs to scrap old license plates dating to before a 1998-99 guerrilla uprising that led to independence.

For a second day on Sunday, trucks and other heavy-duty vehicles blocked several main roads in northern Kosovo that lead to two border crossings with Serbia. Both crossings were closed to traffic.

Late on Saturday Kosovo police said they came under fire in different locations close to a lake bordering Serbia. The force said it had to return fire in self-defense and there were no immediate reports of injuries.

"The barricades from masked criminals in the north must be removed immediately," Kurti said in a statement adding that his government was in contact with NATO's peacekeeping mission that has more than 3,000 troops on the ground.

Police in Pristina said former policeman Dejan Pantic was arrested for allegedly attacking state offices, smashing the windows of the election commission offices, and police officers and election officials Tuesday.

Serb mayors in northern Kosovo municipalities, along with local judges and some 600 police officers, resigned last month in protest over a government decision to replace Belgrade-issued car license plates with ones issued by Pristina.

Serbia's President Aleksandar Vucic said his country would ask NATO's KFOR peacekeeper mission to let Serbia deploy troops and police in Kosovo, although he acknowledged there was no chance of permission being granted.

"We do not seek conflict, but dialogue and peace. But let me be clear: the Republic of Kosovo will defend itself – forcefully and decisively," Kurti said replying Vucic's comments.

Kosovo declared independence from Serbia in 2008 with the backing of the West, following a 1998-1999 war in which NATO intervened to protect Albanian-majority Kosovo.