Facebook has blocked articles by Russian news agencies claiming police last month arrested alleged Ukrainian nationalists after experts concluded the radicals were Russian.

RBK and Kommersant published articles in February reporting that Russian law enforcement had arrested alleged members of MKU, a Ukrainian nationalistic youth organization, in the southwestern city of Voronezh.

Police reportedly discovered extremist literature, symbols of nationalist organizations, knives, and an object resembling on old military mine inside their apartments.

Citing Russia's Federal Security Service (FSB) press service, the news agencies reported their connection to a Ukrainian extremist organization.

However, Russia's Investigative Committee published a release at the time saying simply that three individuals aged 18, 19, and 33 had been arrested for stirring up racial animosity in Voronezh, which lies near the border with Ukraine.

It made no claim that they were members of a Ukrainian nationalist group.

StopFake, a Ukrainian agency that works with Facebook to find and block Russian disinformation on its platform, said its research concluded the three people arrested in Voronezh all belong to a Russian nationalist organization.

StopFake said it contacted Ilya Bichyov, the lead investigator on the case in Voronezh, who declined to comment on whether the three individuals had any connection to Ukraine on the grounds the investigation is continuing.

StopFake, which was created in 2014 by journalism students and faculty members, has itself been accused of ties to Ukrainian far-right groups, something it vehemently denies.

Russia's media watchdog, Roskomnadzor, on March 7 demanded that Facebook unblock the links to the article on its platform, accusing the U.S. social-media company of censorship.

Russia has tried to play up the actions of Ukrainian nationalist groups in an effort to justify its hostile actions toward its neighbor.

Russia annexed Crimea in 2014 and continues to back separatists in eastern Ukraine in a war that has killed more than 13,000 people.

With reporting by RBK