REFILE - ADDING NAME Alexander Vinnik, a 38 year old Russian man (L) suspected of running a money laundering operation, is escorted by a plain-clothes police officer to a court in Thessaloniki, Greece July 26, 2017. REUTERS/Alexandros Avramidis

MOSCOW (Reuters) - A Russian national arrested in Greece on Wednesday on suspicion of laundering criminal funds by switching them into bitcoins is a key person behind the BTC-e crypto-currency exchange, two sources close to the exchange told Reuters.

BTC-e, one of the oldest trading platforms for digital currencies, did not immediately respond to a request for comment.

Police sources identified the man as Alexander Vinnik, 38, who was arrested in northern Greece on a U.S. warrant and is accused of laundering at least $4 billion.