Twenty-nine major Chinese websites have promised to better manage the comments of their users as authorities call for a clean Internet.

Representatives from the 29 web portals, including Tencent.com, Sohu.com, 163.com and the official website of Xinhua News Agency, signed the letter of commitment at a meeting organized by the Cyberspace Administration of China (CAC) on Thursday.

These websites promised to ensure that "their users register, post and write comments with their real identity," according to the commitment letter.

They also "promise to and sincerely ask all users to consciously abide by the'seven bottom lines' -- law and rules, socialist systems, national interests, citizen's legitimate rights, social public order, morality and authenticity of information -- when posting."

The letter asks them to remind web users not to release 18 categories of information that "are against basic principles established by the Constitution," such as information jeopardizing national security, leaking national secrets or instigating ethnic hatred or discrimination.

Web users will be warned, suspended from releasing content, and may have their posts deleted and accounts shut down if they violate regulations. They may also face judicial investigation if their release of information is deemed criminal.

"The management of posts and comments in line with the law concerns the guidance of online public opinion," said deputy CAC director Ren Xianliang, adding that it is key to "administering the Internet according to law."

Websites are responsible for users' posts and comments, said Ren, adding many foreign websites have formulated detailed rules for online release and made the rules and other management measures conspicuous to users.