Russia’s FSB security service said Friday that it arrested more than 20 people in a series of raids targeting illegal cryptocurrency exchanges operating out of offices in the Moscow City financial district.

Together with Russia’s Interior Ministry, the FSB targeted nine unauthorized financial channels accused of laundering money stolen from Russian citizens by phone fraudsters.

The FSB claimed Ukraine-based scam call centers used gray-market exchange offices in Moscow City to convert stolen cash into cryptocurrency and funnel it out of Russia.

In an FSB video shared by state media, one of the individuals arrested in law enforcement raids said that up to $2 million was laundered through their office in a single day.

Some of those arrested claimed on camera that they believed they had been working as undercover informants for either the FSB or Russia’s financial watchdog, Rosfinmonitoring.