A Russian antiwar group in Serbia said Tuesday that authorities have refused to extend the residence permit of one of its activists, a critic of Russian President Vladimir Putin.

The Russian Democratic Society said one of its founders, Vladimir Volokhonski, had all the necessary documentation but the authorities cited a security risk as the reason for their decision.

Serbian police have not commented. A copy of a police document provided by the Russian group said a security assessment of Volokhonski's case showed unspecified "obstacles" for the extension of his stay.

Earlier this month, Serbian police temporarily banned entry to another prominent Russian antiwar activist, Peter Nikitin, who was forced to spend more than a day at the Belgrade airport before he was allowed in.

PUTIN ENFORCES UKRAINE 'RED LINE,' NOW AIMS TO CREATE 'AS MUCH SUFFERING AS POSSIBLE' WITH GRAIN STRIKES

Europe Fox News graphic

A Russian antiwar activist is facing residency permit refusal in Serbia due to a security risk.  (Fox News)

CLICK HERE TO GET THE FOX NEWS APP

The Balkan nation has maintained friendly relations with Russia and has not joined Western sanctions against Moscow, despite condemning its invasion of Ukraine.

The United States recently imposed sanctions against Serbia's pro-Russia intelligence chief, Aleksandar Vulin, accusing him of crimes and corruption. Serbian media have reported that Vulin wiretapped a Russian opposition meeting in Belgrade in 2021, which he has denied.

Volokhonski, an opposition politician from St. Petersburg, fled to Serbia after the start of Russia's invasion of Ukraine, his organization said. His return to Russia would mean imprisonment, the group said.

About 200,000 Russian citizens are believed to have fled to Serbia since the start of the war as the fellow-Slavic nation does not require visas for Russians.