Chinese censors have blocked the U.S. ambassador's name from searches on a microblogging website after he was spotted at a pro-democracy gathering last weekend.

China has tightened control over the Internet in the wake of the unrest sweeping through the Middle East, underscoring the Communist Party's anxiety over the easy spread of information that might challenge its one-party rule.

The online censorship coincides with a rash of detentions after an overseas Chinese-language website, Boxun, spread a call for Jasmine Revolution gatherings to press the Communist Party to make way for democratic change.

Ambassador Jon Huntsman, tipped as a U.S. presidential candidate and who has sparred with China on human rights, was spotted in a crowd at one such gathering on Beijing's Wangfujing shopping street last Sunday.

A video that was later posted on YouTube showed him talking to an unidentified person.

Huntsman's chances of running for the Republican presidential nomination appeared to increase early this week when a group advocating his candidacy launched a fund-raising effort.

Besides Huntsman's Chinese name, searches for the words Egypt, jasmine, jasmine revolution and Hillary Clinton prompted a message saying the results could not be found on the microblogs of Chinese Internet portal

Authorities are particularly worried that people who use online microblogs -- 125 million and growing -- could use them to mobilize.

But search results for Huntsman and Clinton could still be found on less popular Internet chatroom and another Chinese microblogging site run by

The Chinese microblog feed of Huntsman on Tencent Holdings' QQ, another Chinese Twitter-like website, was still accessible.

Last week, China's Internet censors deleted U.S. Embassy posts promoting Secretary of State Hillary Clinton's speech on Internet freedom from microblogs.

It is unclear whether their removal was ordered by the government or censored by the company that hosts the microblogs,, which cooperates with the government under Chinese law to scrub content that is deemed illegal.

Twitter itself is blocked in China, along with Facebook and other websites popular abroad.

Chinese state media has limited coverage of the unrest in Egypt.

And access to the professional networking site LinkedIn was disrupted in China Thursday, following online calls on other sites for more gatherings every weekend in China.

(Reporting by Sui-Lee Wee and Huang Yan, Editing by Ken Wills and Jonathan Thatcher)