Tensions have again flared up between Serbia and Kosovo, prompting the chief of EU’s diplomacy to intervene by calling both sides to show “calm, wisdom, restraint, and leadership”.

Mogherini made her remarks after an urgent meeting with Serbian President Aleksandar Vucic in the Serbian capital of Belgrade.

The US State Department also said in a statement late on March 27 that the United States “strongly condemns” the arrest and expulsion of a Serbian official from Mitrovica on March 26, events that it said “unnecessarily heighten tensions and threaten regional stability.”

Earlier in the day, politicians representing Kosovo’s Serbian minority announced the decision to leave the Pristina government after they met with Vucic in Belgrade, saying they will no longer support Prime Minister Ramush Haradinaj’s cabinet.

Haradinaj called their decision to pull out “incomprehensible” and insisted that his team “will not fall.”

Serbs have also parked trucks to block a key road linking northern Kosovo with the capital.

On Monday, special units of Kosovo police detained the director of the Kosovo office in the Serbian government, Marko Djuric, for alleged illegal entry into Kosovo.

Djuric was detained in Mitrovica North as he was in a meeting with local Serbs. Djuric, who is the head of the Serbian government’s office for Kosovo, was transferred to a court in Pristina before being expelled from the country.

Officers also fired tear gas to disperse a crowd of ethnic Serbs protesting against the arrest.

Russia’s Foreign Ministry said Moscow “strongly” condemned the incident in Mitrovica, alleging that it was “aimed at intimidating Kosovo Serbs.”

A day of EU-brokered negotiations between the leaders of Kosovo and Serbia had broken up late on March 23 without any reported progress on efforts to normalize relations.

Serbian President Aleksandar Vucic did not appear at a news conference immediately after the meeting, but he later on Serbian TV Pink accused Kosovo of stalling the implementation of a 2013 agreement on special rights for municipalities with a majority Serbian population.