HONG KONG — One of the world’s largest cryptocurrency exchanges said it would close all user accounts in mainland China by the end of the year, days after the country’s central bank declared all crypto-related transactions illegal.

Huobi Global, which was founded in 2013 and currently operates from offices in Singapore, South Korea, the US and other countries, over the weekend said it stopped allowing new customers in mainland China to register accounts. The exchange will also gradually retire existing accounts in China by the end of 2021 to ensure the safety of its customers’ assets, it added.