Ukraine's consulate in Rostov-on-Don has sent a written letter to Russian authorities demanding to know the circumstances and reason behind the arrest of Ukrainian citizen Roman Ternovsky.

"Ukraine's consulate today sent a note to Russian competent agencies demanding an immediate explanation of the circumstances and reasons for the arrest, the place of detention, as well as permission for Ukrainian diplomats to visit [Ternovsky]," Ukraine's Foreign Ministry representatives said in Kyiv on Wednesday.

As earlier reported, Russian FSB Security Service agents said they arrested Ternovsky in Rostov region, Russia, and that he was engaged in activities involving Ukraine's Right Sector organization.

"It has been established that Ternovsky is a member of the ultra right-wing Right Sector organization and took part several times in pickets, meetings and other events in Ukraine. In addition, with the assistance of social media platforms, he advertised Right Sector activities on the Internet," Russia's investigation committee said on Wednesday.

The activities of Ternovsky are actionable pursuant to Part 2 of Article 282.2 of the Russian Criminal Code (organizing activities of an extremist organization).

During a search of Ternovsky's residence in Rostov-on-Don clothing and other personal items with Right Sector logos was found.

Ternovsky is currently under arrest.