Sergei Sokolov
© Komsomolskaya Pravda / YoutubeSergei Sokolov
The late Russian billionaire Boris Berezovsky's former head of security has been arrested on an illegal arms possession charge and is being questioned for his role in allegedly planning terrorist attacks.

Berezovsky, the self-exiled tycoon and former powerful Kremlin insider who helped President Vladimir Putin gain power, died in 2013.

Sergei Sokolov was arrested on Tuesday as part of an investigation into an alleged cover-up of organized crime by senior law enforcement officials in the Russian city of Samara, the RBC business portal reported.

"The detained are being inspected for their role in the organized criminal group," the unnamed FSB source said.

RBC reported last year that Sokolov's wife was detained in Ukraine on suspicion of offering work in Russia to former Ukrainian soldiers, who were going to be framed as plotting terrorist attacks in Moscow and other Russian cities, according to Ukraine's National Security Service.