Serbian Government Office for Kosovo and Metohija Director, Marko Djuric said that in case Pristina forms an army, KFOR and NATO would have to disarm it immediately, Tanjug news agency reported.

“Forming of the so-called army goes directly against entire Serbia.” Djuric added.

He reminded that article 9, point B of the UN SC Resolution 1244 clearly says it is the obligation of KFOR and NATO “to demilitarize so-called Kosovo Liberation Army and other armed groups of Kosovo Albanians.”

Chairman of the Serbian Assembly Committee for Kosovo and Metohija, Milovan Drecun warned that KFOR activities do not contribute to the stabilization of the situation, Tanjug news agency reported.

He urged the command of this military mission to explain why last night around 20 trucks came to the base near Mitrovica South.

KFOR has announced it would carry out “some exercises” in the north of Kosovo during the coming days, B92 reports.

“In the following days KFOR is going to conduct some exercise in Northern Kosovo. KFOR troops will move and deploy along the major roads in accordance with their mandate under the UNSCR 1244.This is a normal training activity, not related to any specific threat or concern,” KFOR wrote on their Facebook page.”

“The situation is under control and KFOR continue protecting all citizens in Kosovo, as it has done since 1999,” the statement concluded.

The NATO-led KFOR declared as legal the Kosovo police operation in the northern part of the divided Mitrovica town with the majority of Serbs, during which four men were arrested in connection to the investigation into a Serb politician murder, a Force's statement said on Friday

Serbian President Aleksandar Vucic and Prime Minister Ana Brnabic have asked China's Ambassador in Belgrade, Li Manchang to inform the Chinese leadership that Serbia “has never been in a more difficult situation.”

Ambassador Li responded to this by saying he will notify the President of China about the issue in the course of the day.

Vincenzo Grasso, KFOR spokesman, told TV Prva that KFOR was informed that four people were arrested in Kosovo, but that there is no accurate information about where they are.

"The Kosovo police arrested several people in connection with the murder of Oliver Ivanovic. We were informed that four people were arrested and I'm not sure where they are right now, but I'm sure that they are in the police and would be brought to the justice," Grasso told TV Prva.

An unscheduled closed session of the Serbian Government was held in Belgrade on Friday morning due to the incursion of a Kosovo police unit into the north of Kosovo, reports Serbian media.

President Aleksandar Vucic has had extraordinary meetings with the army and police chiefs this morning. Other security services, as well as commanders of special military and police units, also took part in these meetings.

Nebojsa Covic, former head of the Coordination Centre for Kosovo and Metohija told Prva TV, Kosovo Albanians would not be able to carry out police action this morning, if they had no support from the outside. “Nothing happens without knowledge of Washington,” Covic said.

“That is the pattern. You create new problems, and everything else is pushed aside. Who still remembers the “Yellow House” case, the Brussels agreement, Community of Serb-majority Municipalities, Special Court for KLA war crimes?” Covic asked.

Mayor of Mitrovica North, Goran Rakic told Prva TV three persons were arrested in this town early this morning, including Kosovo police officer and two citizens. All of them are Serbs. Rakic also added, arrested persons were brutally beaten up.

According to Rakic, the excuse used for action was that the arrests are made in relation to Oliver Ivanovic’s murder, however Rakic doubts this version and believes it is about diverting attention from yesterday’s events.

Speaking at a gathering in Belgrade on Thursday, a NATO representative said the alliance was "not against" an army being formed in Kosovo army.

But that this must be done in accordance with the (Kosovo) Constitution, said Robert Pszczel, a senior officer for Russia and the Western Balkans from NATO's Public Diplomacy Department (PDD).