Billionaire Alexander Lebedev, owner of Britain's Independent newspaper, has been held inside the Moscow headquarters of a bank he owns while masked police rifled through company files.
A spokesman for Mr Lebedev said around 30 armed officers surrounded Mr Lebedev's National Reserve Bank before they entered.
He said he knew of no reason for the raid.
A police spokesman refused to comment.
Mr Lebedev recently bought the Independent and also owns the London Evening Standard. He has a stake in Russia's Novaya Gazeta newspaper and is part-owner of national airline Aeroflot.
Raiding company property and seizing computers and documents is common practice among Russia's law-enforcement agencies.
Security guards said later that the search was over and that police had left.