(Bloomberg) -- Serbia, a candidate nation for European Union membership, should rethink continuing cooperation with the Kremlin as a recent bilateral deal with Russia raises serious questions, an official for the bloc said.

Russia’s Foreign Minister Sergei Lavrov and his Serbian counterpart Nikola Selakovic signed a two-year plan on mutual consultations last week. Some opposition groups in Serbia slammed the government, which has close ties with Vladimir Putin, for signing such a document while the war in Ukraine rages.

The “decision to coordinate foreign policy is a sign of the intention to further strengthen relations between Serbia and Russia, and this is raising serious questions,” EU spokesman Peter Stano said. “Relations with Russia cannot be business as usual, we are taking this very seriously.”

Serbia has condemned the invasion of Ukraine but stopped short of joining the punitive international sanctions against Russia. Serbia’s foreign minister dismissed the concerns, describing the deal with Moscow as “a technical thing” routinely renewed every two years.

Still, Serbia doesn’t recognize the Russia-backed referendums in eastern and southern Ukraine, Selakovic said on Sunday. Ukraine’s official borders must be respected, just as Serbia insists that Kosovo remains part of its territory, he said.

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