Serbian President Alexander Vucic said Monday he was not surprised to see obstacles to Russian Foreign Minister Sergey Lavrov's visit to Belgrade, noting that his country was subject to mounting pressures.

Lavrov’s visit to Belgrade was scheduled for June 6-7, but the countries neighboring Serbia have closed their airspace to Lavrov's flight.

"I am not surprised that the visit has been postponed. There were attempts to change the route, countries that forbade the flight of the plane of the head of the Russian Foreign Ministry," Vucic said.

Vucic told Radio Television of Serbia, "you will express dissatisfaction and disagreement with the attempts to ban the conversation, and, above all, in connection with the atmosphere, in connection with the visit of Sergey Lavrov to Belgrade."

While the European Union tries to further isolate Russia and minimalize energy imports from the country, EU candidate Serbia is improving ties with Moscow through a new gas supply deal. 

Belgrade condemned Russia's military advancement in Ukraine at the United Nations but refused to impose sanctions against what it considers "an old ally," even if the country aims to join the EU.

A three-year natural gas contract was signed between Belgrade and Moscow a day before the Europeans voted to ban most Russian oil imports this week, prompting a reprimand from Brussels.

EU Spokesperson Peter Stano said the bloc expects Serbia "not to further strengthen its ties with Russia". "Candidate countries, including Serbia, are expected to progressively align their policies towards third countries with the policies and positions adopted by the European Union, including with restrictive measures," Stano said in a statement.