Serbia has abruptly recalled all staff from its embassy in Macedonia for consultations regarding "offensive intelligence activities" against Serbia, President Aleksandar Vucic has said.
No reason was initially given for the move, but Vucic later told reporters in Serbia that the decision was based on "sufficient evidence of highly offensive intelligence activities against certain bodies and institutions of Serbia."
"Our duty is that our people be prepared and ready. There will probably be some changes in our staff to protect the friendship between Serbians and Macedonians," he added.
Vucic spoke about "a different and new environment" in Macedonia, and said things would become clearer in coming days.
Serbian Foreign Minister Ivica Dacic told Serbian media that part of the embassy staff will return to Skopje next week.
Macedonian media reports suggested the decision was linked to Skopje's alleged decision to back a potential new bid by Kosovo to join UN's cultural body, UNESCO.
Serbia has not recognized Kosovo's independence claim and opposes its attempts to join international organizations.
Kosovo, which declared independence in 2008, applied to join UNESCO in 2015, but its application did not secure enough votes.
Kosovo has not yet reapplied ahead of a UNESCO general meeting in two months.
When asked if the embassy withdrawal was related to a UNESCO bid, Vucic did not answer directly but said relations with Skopje "must be based on mutual respect."
"Our job is to protect the interests of Serbia without disrupting the interests of other countries," he said.
Macedonia's government, which came to power in late May, said in a statement that it was "developing friendly relations" with its neighbors.
"With regard to the vote on Kosovo's accession to UNESCO, the Macedonian government will take into account the positions of the majority of EU countries," the government said in a statement.
Relations between the two former Yugoslav republics have been strained since this year's transition of power in Skopje.
Macedonian Prime Minister Zoran Zaev's coalition government took power in May, almost six months after general elections.
Before assuming office, Zaev accused the Serbian leadership of promoting nationalism.
Dacic described the statement as a "brutal and scandalous attack" on then-Prime Minister Vucic and his government.