The entire staff of the Serbian Embassy in the Macedonian capital has been withdrawn for urgent consultations in Belgrade in a move that has further strained relations between the Balkan neighbors.
Serbian President Aleksandar Vucic said Monday that the withdrawal was made after intelligence reports of "very offensive acts" planned against Serb interests in Macedonia. He didn't specify, adding that in the next 10 days "everything will be much clearer."
The Macedonian Foreign Ministry said Monday it "is not aware of the reasons for this decision." Macedonian media said that Sunday night's move was made after Macedonia indicated it would support another bid by Kosovo for membership in the United Nation's education, cultural and scientific organization, UNESCO.
The Macedonian government said in a statement that it wants good relations with Serbia, but will vote in line with a majority of European Union countries on Kosovo's UNESCO membership. Macedonia is a candidate for EU membership.
Most EU countries have recognized Kosovo's statehood since it declared independence from Serbia in 2008 and are likely to support its bid to join UNESCO. Serbia rejects Kosovo's independence and is trying to block any of its attempts to join international institutions.
UNESCO's member states narrowly rejected Kosovo's bid for membership two years ago, a victory for Serbia and its ally Russia and a blow to Kosovo's goal of obtaining global recognition as a state.
"We want to build good relations with Macedonia, but it is our duty to protect our interests," Serbian Foreign Minister Ivica Dacic said.
Dacic said an unspecified "foreign factor" was involved in the "offensive" acts against Serbia and that "a part" of the embassy staff will return to Macedonia next week.
Macedonia's position to follow the majority of EU member states when voting on Kosovo membership in UNESCO will "directly impact good neighbourly relations," Dacic told Tanjug news agency.
Vucic himself said that Belgrade would continue to develop good relations with Macedonia but "these relations will have to be based on mutual respect."
Maintaining good relations with neighbours is a key requirement for the six Western Balkan states including Kosovo, Macedonia and Serbia, to make progress towards desired EU membership.
Nearly one-third of Macedonia's population is ethnic Albanian.
Relations between Serbia and Macedonia have been strained since Macedonia Prime Minister Zoran Zaev formed his coalition government with ethnic Albanian parties this spring, almost six months after a parliamentary election.
In April, following media reports that a Serbian intelligence officer had been in the Macedonian parliament when protesters stormed the building and beat up several deputies including Prime Minister Zoran Zaev, the eelations between Serbia and Macedonia were further strained.
Both Serbia and Russia have voiced support for Macedonia ex-Prime Minister Nikola Gruevski's conservative VMRO-DPMNE party. The party placed first in the election, but without winning a governing majority.
Russia is opposed to Zaev's plans for Macedonia to join NATO and to speed up its EU membership bid.
Serbia and Macedonia were part of the former Yugoslav federation that broke up in a bloody civil war in the 1990s.
Kosovo, a former Serbian province, declared independence in 2008 nearly a decade after NATO air strikes that ousted Serb forces and halted a bloody two-year crackdown on ethnic Albanians.
Though Kosovo is recognised by 114 countries, including Macedonia and 23 European Union members, Serbia's allies, Russia and China, are still blocking its full membership of the United Nations.