Serbian troops stationed along its border with Kosovo have been put on full combat readiness, "the highest level" of alert, Defense Minister Milos Vucevic said Monday.

The development, ignoring NATO's calls for calming down of tensions, highlights the Balkan country's increasingly strained relations with neighboring Kosovo over recent shootings and blockades.

Kosovo declared independence from Serbia in 2008, but Belgrade has refused to recognize it and encouraged Kosovo's 120,000 ethnic Serbs to defy Pristina's authority – especially in the north where ethnic Serbs make up the majority.

The Serbian army has been put on a heightened state of alert over tensions with Kosovo multiple times in recent years – the last time in November after claiming that several drones entered Serbian airspace from Kosovo.

On Dec. 10, Serbs in northern Kosovo set up barricades to protest against the arrest of an ex-policeman suspected of being involved in attacks against ethnic Albanian police officers.

The blockades have coincided with a rise in reported shootings, the latest on Sunday, according to NATO-led peacekeeping force KFOR.

"Serbia's president ... ordered the Serbian army to be on the highest level of combat readiness that is to the level of the use of armed force," Defense Minister Milos Vucevic said in a statement.

He added that President Aleksandar Vucic also ordered the special armed forces to be beefed up from the existing 1,500 to 5,000.

Serbia's Interior Minister Bratislav Gasic said he "ordered the full combat readiness" of police and other security units and that they be placed under the command of the army chief of staff according to "their operational plan."

He said in a statement that he acted on the orders of Serbian President Aleksandar Vucic so that "all measures be taken to protect the Serbian people in Kosovo."

These orders from Vucic come after army chief Gen. Milan Mojsilovic was dispatched to the border with Kosovo on Sunday.

"The situation there is complicated and complex," Mojsilovic said Sunday.

It was not immediately clear what this order meant on the ground as Serbian troops have been on alert for a while on the border with Kosovo.

Defying authorities

Northern Kosovo has been especially on edge since November when hundreds of ethnic Serb workers in the Kosovo police as well as the judicial branch, such as judges and prosecutors, walked off the job.

They were protesting a controversial decision to ban Serbs living in Kosovo from using Belgrade-issued license plates – a policy that was eventually scrapped by Pristina.

But the mass walkouts created a security vacuum in Kosovo.

Pristina attempted to schedule the Dec. 18 local elections in Serb-majority municipalities – but it was postponed after the announcement caused widespread outrage and the main Serb political party said it would stage a boycott.

Then on Dec. 10, an ex-policeman suspected of involvement in attacks against ethnic Albanian police officers was arrested, outraging ethnic Serbs who erected the barricades that paralyzed traffic around two border crossings.

Just hours after the barricades were erected, Kosovo police said they suffered three successive firearm attacks on one of the roads leading to the border.

KFOR, which has increased its presence and patrols in the region in recent months, said the latest bout of violence came Sunday, when shots were fired in the direction of Latvian soldiers embedded with the force, Kosovo's defence ministry tweeted.

KFOR said it was investigating the incident, and added there were "no injuries or material damage."

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

But Kosovo's Security Council – which met Monday – blamed Serbia for the latest deterioration in relations.

It accused Serbia of "acting with all available means against the constitutional order of the Republic of Kosovo".

Serbs account for about 120,000 of Kosovo's 1.8 million population, which is predominantly ethnic Albanians.

Kosovo remains a potential flashpoint in the Balkans years after the 1998-99 war that ended with NATO intervention. Serbia doesn't recognize the 2008 declaration of independence of its former province, while Western efforts to mediate a solution so far have failed.

"It is important for all involved to avoid any rhetoric or actions that can cause tensions and escalate the situation," KFOR said in a statement.

"We expect all actors to refrain from provocative shows of force and to seek the best solution to ensure the safety and security of all communities."

Fears of violence have soared since the start of Russia's war in Ukraine. The United States and most European Union countries have recognized Kosovo's independence, while Serbia has relied on Russia and China in its bid to maintain claim on the province.