WASHINGTON, March 17 (UPI) -- The Chinese authorities' crackdown on Tibetan protests spread to the Internet at the weekend, with censors blocking YouTube and other sites as the Dalai Lama accused the regime of "cultural genocide" against his people.

Chinese authorities blocked access to the U.S.-based video-sharing Web site YouTube at the weekend after users uploaded dozens of videos of the protests in which Buddhist monks and other Tibetan protesters clashed with Chinese authorities, leaving dozens of police injured and an unknown number of protesters dead.

There were no such videos available from China-based video-sharing sites, such as youku.com. Last month 50 such sites were required by the State Administration of Radio Film and Television to sign a "self-discipline agreement," according to Marbridge Consulting, a market research firm specializing in China's telecommunications and IT sectors.

Tudou.com, which refused to sign, had its cooperation with state-run TV put on hold and is now awaiting possible punishment, said Marbridge. The site was offline for 24 hours Friday, the result of what its administrators said was a server move, but other observers said was probably an emergency review by SARFT to check for possible Tibet-related content.

In a statement e-mailed to United Press International, YouTube said it had seen "reports of users being unable to access" the site in China. "We are looking into the matter, and working to ensure that the service is restored as soon as possible," the statement said.