Serbia's president sent his army chief to the border with Kosovo as ties between the squabbling neighbours further degenerated after recent roadblocks set up in Kosovo's Serb-majority north.

Kosovo declared independence from Serbia in 2008, but Belgrade refuses to recognise the move and encourages the remaining 120,000 Serbs to defy Pristina's authority.

Serbian army chief General Milan Mojsilovic said on Sunday that "the situation there is complicated and complex" and added that "the presence of the Serbian army along the administrative line," or border, was needed.

Hundreds of ethnic Serbs, outraged over the arrest of an ex-police officer, set up roadblocks on December 10 in Serb-majority northern Kosovo, paralysing traffic through two border crossings.

The general said late Sunday he was on his way to Raska, a town about 10 kilometres (six miles) from the border after meeting with President Aleksandar Vucic in Belgrade.

"The tasks the Serbian army has got ... are precise, clear, and will be fully implemented," Mojsilovic said.

Shortly before Mojsilovic left for the border, several Serbian pro-government media outlets aired a video in which gunfire can be heard.

The outlets said it was "fighting" that occurred on Sunday evening when Kosovar forces tried to dismantle a barricade.

This was rejected by Kosovar police in a Facebook post.

The NATO-led peacekeeping force KFOR said it was investigating an "indirect fire incident on 25 December in the close proximity of a NATO KFOR patrol" that involved an unknown number of armed people.

"There were no injuries or material damages, and we are working to establish all the facts," KFOR said in a statement.

The latest bout of tensions came after Kosovo scheduled local elections in Serb-majority municipalities which the main Serb political party said it would boycott.

An ex-policeman suspected of involvement in attacks against ethnic Albanian police officers was arrested, outraging ethnic Serbs who erected the barricades.

In November, hundreds of ethnic Serb police officers embedded in the Kosovo police -- as well as judges, prosecutors and other officials -- walked off the job to protest against a controversial decision to ban Serbs living in Kosovo from using Belgrade-issued licence plates.

This was then scrapped by Pristina but the mass walkouts created a security vacuum in Kosovo.

Serbian Prime Minister Ana Brnabic said last week the situation with Kosovo was "on the brink of armed conflict".