Social networking sites like Facebook pose a security threat to China and are used as "tools of subversion" by Western nations including the US, a top Chinese think tank said in a report this week.

Ethnic riots in China's western-most Xinjiang region last year were spurred on by such micro-blogging sites, the state-run China Academy of Social Sciences (CASS) said in its annual report on the development of new media.

"Facebook has appeared as the rallying point for overseas Xinjiang separatist groups," the report said.

"These social networking sites have become a tool of political subversion used by Western nations, including the United States."

Social networking sites like Facebook and Twitter are blocked in China.

Ethnic Uighur Muslims battled Han Chinese in the streets of the Xinjiang capital of Urumqi in July last year leaving over 200 people dead and some 1,700 injured in China's worst ethnic violence in decades.

Following the unrest, the authorities shut down the Internet in Xinjiang for nearly a year.

"Faced with the popularity of social networking sites ... it is imperative to exert control," the report, published this week said, adding that China ought to "pay a lot of attention to these potential risks and latent dangers."

Despite blocking Facebook, Chinese micro-blogging sites, like Kaixin, remain popular and have developed rapidly since 2008, the report said.

It mentioned no potential security threat from such Chinese sites.

At the end of 2009, 176 million Chinese Internet users were using social networking sites, with most between 20 and 29 years of age, according to government figures.

In a separate article, Internet giant Google was portrayed as being tied to US government information services and bent on advancing America's global "hegemony", the CASS report said.

China boasts the biggest online population in the world with over 400 million Internet users.

Chinese authorities keep a tight rein on the Web, blocking unwanted content in a system known as the Great Firewall of China which largely censors subversive political content and pornography.