If you want to block any top-level domain by its name just add this TLD without leading dot into your black list.

In example, if you want to block access to all websites in domain zone RU, then add ru to your black list.

For internationalized country code top-level domains you should add them to black list in the IDN form: 中国 (Chinese IDN ccTLD), рф(Russian IDN ccTLD), etc.

Full list of Internet top-level domains can be seen on IANA website and Wikipedia.