China is cracking down on junk e-mail and "illegal" mobile phone text messages, the official Xinhua News Agency said Tuesday.

A new regulation will ban sending e-mail for advertising purposes to people without their permission, and all advertising e-mail must be titled "advertisement" or "AD," the agency said.

It also said that mobile phones must be registered under users' real names, and that text messaging will be controlled more tightly due to the spread of "illegal messages."

The government was vague on details, however.

For instance, the report did not describe what constituted illegal messages or how they would be controlled, nor did it specify any penalties or say when the new rules would take effect.

It's also not clear how well the rules could be enforced. Several countries and U.S. states have anti-spam laws, yet junk e-mail continues to be an online pest, with much of it coming from or through computers in China and other Asian countries.

China now has 111 million Internet users, second only to the United States, and Xinhua said Tuesday that each e-mail subscriber in China received an average of 16.8 pieces of junk e-mail a week from August 2004 to April 2005.

"China has become seriously affected by junk e-mail," said Li Guobin, an official with the country's Ministry of Information Industry.

On the mobile phone rules, state media already reported in December that China would soon require that all mobile phone users — including the large number who use prepaid phone cards — register with telecom providers or face a service cutoff.

They said the measure was aimed at fighting unspecified telephone fraud, and the use of counterfeit and otherwise illegally obtained mobile phones.

It was also expected to help authorities control "improper political commentary," the December report said.

Furthermore, China published last fall an update to Internet regulations that the state-run China Daily said would cover text messages, a fast and efficient communications means available to anyone with a mobile phone.

It was not immediately clear whether the mobile rules described Tuesday refer to those announced earlier.

Either way, it appears part of China's efforts to discourage protests and restrict dissidents. Analysts say people in China and elsewhere have successfully used text messaging to organize, spread information and rally crowds of protesters.

China's government already operates what is widely regarded as the world's most sweeping effort to monitor and control Internet use, with all online traffic passing through state-controlled gateways.

Filters block access to foreign Web sites deemed subversive or pornographic, and Web sites in China are required to remove prohibited content.

Some U.S. Internet companies and search engines have been criticized by American lawmakers and free-speech advocates for cooperating with Chinese government controls.