Belgrade was on Thursday investigating a video that purports to show a Russian agent providing cash to an unidentified man in Serbia, triggering alarm in the Balkan state.
A Serbian intelligence official confirmed late Wednesday that the video is authentic and identified the Russian agent as Georgy Kleban.
The clip, whose origins are still unconfirmed, shows the Russian meeting in a car park with a man who local media have portrayed as a Serbian intelligence officer.
During the encounter the Russian hands the man a plastic bag. Later the Serb, whose face is blurred, is seen inside his car counting money from an envelope that was in the bag.
"Our services, both civilian and military, are intensely engaged in establishing all the circumstances related to this event," Relja Zeljski, the chief of Serbian intelligence's analytical section, told state-run RTS.
On Thursday President Aleksandar Vucic convened a meeting with the National Security Council over the affair. He is due to visit Moscow on December 4.
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Western countries frequently accuse Russia of meddling in the Western Balkans, a corner of Europe that lies outside of the EU.
Russia rejects the allegations and in turn accuses Brussels and Washington, who have sought to bring the region into the NATO sphere to Moscow's chagrin.
Serbia, which aspires to join the EU, remains one of Russia's strongest allies in the Balkans, with the two countries enjoying a warm cultural bond over their shared Orthodox Christian faith.