The Chinese government has quietly begun preventing access again to Web sites that it had stopped blocking during the Olympic Games in China in August, Internet experts said on Tuesday.

Liu Jianchao, a spokesman for China's Foreign Ministry, said at his semi-weekly news conference on Tuesday in Beijing that the Chinese government had a right to censor Web sites that violate the country's laws. He added that "some Web sites," which he did not identify, had violated China's law against secession by suggesting that there are two Chinas - a reference to the Beijing government's longstanding position that mainland China and Taiwan form a single China.

Comment: It is obviously against China law to have an opinion that differs from the Chinese government. Hmmmm, sounds like what is happening in the West. They must have been taking notes while at the Beijing Olympics!

"I hope that the Web sites in question will be able to self-regulate, and not do things that will violate Chinese law, and for the sake of both sides, develop conditions for Web site cooperation," Liu said, according to a transcript posted on the Foreign Ministry's Web site.

Rebecca MacKinnon, a specialist in Internet restrictions at Hong Kong University, said that the Chinese authorities had recently resumed blocking access to her blog from mainland computers.

"It does appear that in the last week a lot of things got reblocked that were unblocked during the Olympics," she said, adding, "I have not written about the two Chinas issue arguably in the past year; it is not what I focus on."

The government's action comes as the Chinese economy has slowed sharply this autumn. Chinese leaders have begun cautioning about potential risks to social stability caused by high unemployment. Chinese officials have followed a pattern over the years of censoring the Internet more tightly at times of economic or political stress.

Asiaweek, a Hong Kong-based publication, reported this week that the Chinese-language version of its Web site, as well as those of the BBC, Voice of America and Ming Pao, a Hong Kong newspaper, had been blocked since early December.

On its Web site, the BBC reported that a number of foreign Web sites had been blocked and said that it "expressed disappointment at the apparent reinstatement of the ban" since the Olympics. The BBC reported that the Foreign Ministry refused at the news conference to confirm that the government was responsible for blocking access to the Web sites.

But at the news conference, Liu defended China's monitoring of the Internet by saying that other countries also restricted access to some Web sites. The Chinese government "needs to do the required management of Web sites based on the law, just as what other countries are doing," he said. In recent days, Britain and Australia have both moved to limit the distribution of child pornography over the Internet. Germany requires search engines not to show links to Web sites linked to Nazi activity.

But MacKinnon noted that, in contrast to other countries, the Chinese government defines crime very broadly, imposes censorship with little if any explanation and provides no process for operators of blocked Web sites to appeal censorship decisions. She added that even when entire Web sites are not blocked, the Chinese government still sometimes limits certain keyword searches.