As China's online population - the world's largest - surges past the 400 million mark, its Communist government is growing increasingly sensitive to any online threats to its authority. Although Beijing operates an extensive system of monitoring and censorship to block material deemed subversive, the Internet is still the most open and lively forum for discussion in a society where traditional media are controlled by the state.
Twitter, for instance, has emerged as a gathering place for dissidents and other politically minded Chinese wanting to voice their complaints and share information. Though the government routinely bans sites like Facebook, Twitter and YouTube, technologically savvy users can easily jump China's "Great Firewall" with proxy servers or other alternatives.
According to a report released this week by the Chinese Academy of Social Sciences, the sites also harbor an external threat. Social networking sites threaten state security because the U.S. and other Western countries are using them to foment instability, said the report, titled "Development of China's New Media."
"We must pay attention to the potential risks and threats to state security as the popularity of social networking sites continues to grow," the report said. "We must immediately step up supervision of social networking sites."
It cited unnamed U.S. officials as saying that social networking is an "invaluable tool" for overthrowing foreign governments. A comment by U.S. Defense Secretary Robert Gates that new communication technology is a "huge strategic asset" was also given as an example of the U.S. threat.
The report noted how Facebook and other social networking sites were used as tools of "political subversion" in the mass protests following the Iranian elections last year. They also played a role in the violence in China's far-western region of Xinjiang last summer that left some 200 people dead, the report said, noting some online groups overseas had issued calls for independence for the traditionally Muslim area.
A spokesman for the U.S. Embassy in Beijing declined to comment on the specifics of the report because he had not seen it, but said the U.S. viewed freedom of expression as a "universal human right."
"For us, it's an issue of Internet freedom and we're strongly committed to Internet freedom and oppose all forms of censorship," spokesman Richard Buangan said.
Facebook, based in Palo Alto, California, did not immediately respond to an out-of-hours e-mail seeking comment.
Most of the overwhelmingly young Chinese Internet users go online just to chat, play games, listen to music and shop. Government-approved Chinese substitutes for banned sites are readily available: Kaixinwang and Renren instead of Facebook, for example.
But China remains so sensitive to potential threats posed by the Internet that it recently issued a directive banning its troops from having blogs or personal websites, as well as visiting Internet cafes or online dating sites. Military experts said the steps were necessary to avoid compromising security.