British-American financier Bill Browder says he has been arrested in Spain on a Russia Interpol arrest warrant.
Browder, the founder of Hermitage Capital Management, wrote in a tweet that he had been arrested in Madrid by Spanish police and was being taken to a police station.
"In the back of the Spanish police car going to the station on the Russian arrest warrant. They won't tell me which station," the tweet reads.
Browder was found guilty in absentia by a Moscow court in December of large-scale tax evasion of some 3 billion rubles ($48 million) and sentenced to nine years in prison.
His lawyers have appealed the verdict.
Browder, who has led a global push for sanctions against Russian officials implicated in the death of imprisoned Russian whistle-blower Sergei Magnitsky, was also fined 200,000 rubles (about $3,500) and banned from conducting business activities in Russia for three years.
Ivan Cherkasov, Browder's co-defendant, also was given an eight-year sentence in absentia.
Browder and Cherkasov live in the Britain.
Browder has repeatedly dismissed allegations against him as baseless, politically motivated, and revenge for his work to encourage countries to pass legislation similar to the U.S. Magnitsky Act, a 2012 law that imposed visa bans and asset freezes on Russians alleged to be involved in the death of whistle-blowing accountant Magnitsky.
At least five other countries have since implemented sanctions based on the Magnitsky Act.
In December, Browder called for Interpol to "suspend Russia’s membership for flagrant abuse of the Interpol system."