China’s blocking of access to YouTube and other video sites should serve as a warning that government officials in the Asian country have no intention of loosening their grip on negative media coverage as the Olympics approach this summer—despite promises to the contrary.

More likely, the country’s authorities will intensify their control as the major sporting event nears, said U.C. Berkeley Journalism professor Xiao Qiang, an expert on Chinese media censorship.

“Because the Chinese government is facing so much criticism it is trying to control online information and public opinion desperately,” he said.

This weekend, China began restricting access to several popular web sites in an apparent attempt to censor coverage of the violence and protesting in Lhasa, the Tibetan capital.

YouTube, the BBC, CNN, and Yahoo News web sites have been regularly inaccessible, according to Journalists Without Borders, a press freedom group. Photo-sharing site Flickr, Wikipedia, and web sites for British newspapers the Guardian and the Times have also experienced some censorship.

China has a history of censoring web sites that publish political content authorities disapprove of.

Google searches within China for Tiananmen Square, for example, notoriously link to cheery videos or photos—not the infamous picture of a defiant protestor standing down a row of tanks in 1989, according to human rights group Amnesty International.

"Yet again the Chinese government is trampling on the promises it made linked to the Olympics and [is] preparing the ground to crackdown on the Tibetan revolt in the absence of witnesses," said Journalists Without Borders in a statement.

But despite the recent crackdown, the explosive growth of Internet users in China—now numbering more than 200 million—has increased the flow of information in the country, giving ordinary Chinese more ways to express themselves, said Berkeley professor Qiang.