Updated

China widened its Internet policing after online calls for protests like those that swept the Middle East, with social networking site LinkedIn and searches for the U.S. ambassador's name both blocked on Friday.

Searches for Ambassador Jon Huntsman's name in Chinese on popular microblogging site Sina Weibo were met with a message saying results were not available due to unspecified "laws, regulations and policies."

A video circulating online shows Huntsman, who has been mentioned as a potential Republican presidential candidate, scanning the crowd at the site of a tiny protest in Beijing last weekend. An unidentified Chinese man asked Huntsman what he was doing there and whether he wanted to see chaos in China. Huntsman walked away from the scene after that comment.

The U.S. Embassy was aware that Huntsman's name was being "restricted on some searches" on China's domestic Internet, spokesman Richard Buangan said, but declined further comment on the issue.

He said the ambassador and some family members were passing through the bustling Wangfujing shopping street on Sunday and it was a coincidence that they were there at the same time as the planned protest.

Notices that began circulating last week on an overseas website and called for protests in cities across China every Sunday have so far attracted few overt demonstrators but nevertheless unnerved the authoritarian government.

In addition to increased filtering of the Internet, police have also questioned, placed under house arrest and otherwise detained more than a hundred people, the monitoring group China Human Rights Defenders said. At least five have been detained on subversion or national security charges, in some cases for passing on information about the protest calls.

The Beijing police department on Friday, in an unusual move, summoned The Associated Press and several other foreign news organizations for brief meetings to restate regulations requiring foreign reporters to receive permission from government agencies, companies and individuals for interviews.

LinkedIn does not have a strong following among Chinese users, who make up one million of its 90 million-plus members, but the site had previously been accessible. On Friday, it could not be opened within China.

The Mountain View, California-based company said in a statement that the site was blocked for some people and they were continuing to monitor the situation, which was apparently "part of a broader effort in China going on right now."

The appearance of the U.S. ambassador at Sunday's protest feeds into a frequent theme in state-controlled media: that the U.S. is trying to subvert China. One website that focuses on criticizing Western media coverage, anti-cnn.com, said Huntsman's presence at the protest site "obviously reflected" a "coordinated campaign to disrupt China."

The Chinese Foreign Ministry on Thursday sidestepped questions asking whether Beijing believed Huntsman was there by coincidence. Spokesman Ma Zhaoxu said he was not aware of specifics of the case.