HONG KONG (AP) - China will shut down or punish dozens of video-sharing Web sites for carrying content deemed pornographic, violent or a threat to national security under rules that tighten Internet controls, a regulator said Friday.

The announcement came as Chinese Web surfers were blocked from seeing foreign sites with video about protests in Tibet. The new order did not mention the anti-government demonstrations or China's resulting crackdown.

One of China's most popular video-sharing sites, Tudou.com, was among those penalized, the State Administration of Radio, Film and Television said. It gave no details of Tudou's violation or penalty. Other major competitors such as Youku.com and 56.com were not cited.

Rules that took effect Jan. 31 ban Chinese sites from distributing online video that involves national secrets, hurts the reputation of China, disrupts social stability or promotes pornography. Web sites are required to delete and report such content.

Communist authorities have also tightened controls on Chinese media ahead of this summer's Beijing Olympics in hopes of stopping content that might tarnish a national prestige event.

In the recent sweep, regulators ordered 25 Web sites to shut down and will punish 32 others following a two-month investigation, the administration said on its Web site. It gave no details of penalties and phone calls to the office were not answered.

The companies knew the penalties were coming, and they do not appear to be connected to efforts to block footage of the protests in Tibet, said Duncan Clark, managing director of BDA China Ltd., a Beijing consulting firm.

A Tudou.com vice president, Dan Brody, said the site received a warning. He declined further comment.

The industry has grown quickly as a source of news in a country where the government owns all newspapers and broadcasters and enforces the ruling Communist Party's censorship guidelines. Some sites say they get 100 million visitors a day, an audience that rivals that of the biggest state television channels.

Chinese regulators see the profit potential for video-sharing and have tried to strike a balance between enforcing censorship and letting fast-growing sites compete for visitors.

"It's niche no longer, so the party takes the view that it's mass media, so it has to be subject to the same controls," Clark said.

The government announced in December that all video-sharing sites had to be state-owned. But it backed off following warnings that would stifle the industry and said any properly licensed company already operating could continue.

Chinese Web surfers have recently been blocked from seeing YouTube after video about the Tibet protests appeared on the popular U.S. site. Foreign Web sites run by news organizations and human rights groups are regularly blocked when they carry sensitive information.

The potential for video-sharing sites to embarrass the government was highlighted in December when a sportscaster grabbed the microphone and accused her husband of adultery at a state TV event to announce Olympics coverage plans.

A video of the Dec. 28 event appeared on dozens of Web sites in China and abroad. Tudou said it was one of the site's most-watched items.