It is reported by Censor.NET citing the press service of the agency.
According to the report, Popov was trying to enter the territory of Ukraine to support the terrorists.
The day before he told Russian reporters that his Cossacks are travelling to Donetsk and Sloviansk to fight with Ukrainian authorities and urged those who "specializes in armored vehicles" to join him.
As it is well known, "Cossack-fighters" of his accomplice FSB controlled Cossack General Nikolay Kozitsin held the OSCE mission personnel as human shield, mined roads and bridges, attacked the Ukrainian border guards, provided corridors for delivery of arms and mercenaries from Russia to the Donbas.
Popov is being checked on involvement in terrorist activities in Ukraine.