Tensions between Serbia and Montenegro escalated on the eve of an EU–Western Balkans summit in Tivat, as Serbian President Aleksandar Vučić travelled to the host country despite warnings over threats to his safety and a string of cross-border incidents.

Serbia’s Security and Information Agency (BIA) advised Vučić not to attend the June 5 summit in the coastal town of Tivat, citing intelligence on “hostile activities of foreign services” and the presence of organised crime figures. 

Vučić said on June 4 that it was “no secret” that criminal clan leaders from Montenegro had tried to have him killed in 2021, Tanjug reported.

Vučić said he would attend the conference regardless, stressing it was important for Serbia to be represented at the gathering of European Union and Western Balkans leaders.

The warning from the BIA came after Montenegrin authorities blocked 87 Serbian men from entering the country on June 3 after they arrived on a charter flight from Belgrade, saying they posed a risk to national security.

Police said some of the men had been linked to violent offences and high-risk public gatherings (likely referring to recent clashes between pro- and anti-government protesters in Serbia). Two buses believed to have been arranged to transport the group were also seized. 

A police source quoted by Vijesti suggested the group’s arrival could be linked to a “hybrid operation”. Local media published photographs of physically-imposing, heavily-tattooed men waiting at the airport, suggesting they were pro-government thugs sent to cause trouble.

Vučić denied such allegations, telling reporters on June 4 that the men had done nothing wrong and had been illegally barred from entering the country. “These people haven't committed any crime. None”,  Tanjug quoted.

The incident was followed by retaliatory measures at the border, with Serbian authorities tightening checks on travellers from Montenegro on June 3. Montenegrin officials said some of their citizens were denied entry or temporarily detained at crossings.

Montenegro’s foreign ministry said it had sought clarification from Belgrade after receiving multiple complaints from citizens.

Relations between Belgrade and Podgorica have been strained in recent years over Montenegro’s recognition of Kosovo, which Serbia does not accept, as well as allegations from Podgorica of Belgrade’s interference in domestic politics through the Serbian Orthodox Church and parties linked to Vučić’s Serbian Progressive Party.

Montenegro, which became independent from its union with Serbia in 2006, is a NATO member and has aligned its foreign policy with the European Union, including by imposing sanctions on Russia. Serbia, by contrast, has maintained closer ties with Moscow and has not joined Western sanctions.

The summit, due to be held on June 5 under the theme “Shared Prosperity and Stability of the EU and the Western Balkans”, is expected to focus on enlargement and regional stability. French President Emmanuel Macron, German Chancellor Friedrich Merz and European Commission President Ursula von der Leyen are due to attend.