BEIJING -- China's central bank said Thursday it is confident of continuing to expand the pilot program of digital yuan for which the upcoming Beijing Winter Olympics will be an important test scenario.

Currently, digital yuan service is offered mainly by invitation and the number of clients on the whitelist has reached 10 million, Fan Yifei, deputy governor of the People's Bank of China, told a press conference.

Private digital currencies, especially bitcoin, have become speculative tools and means of money laundering for illegal economic activities, posing risks to financial security and social stability, said Fan.

The central bank has taken measures against private digital currencies and is observing and studying them, Fan added.