Pornography websites and other pages that were previously blocked by China's Internet censors were accessible inside the country Friday, though reasons for the change were unclear.

Beijing encourages Internet use for business and education but tries to block material deemed subversive or pornographic and operates an extensive system of Web monitoring and censorship. The government has launched repeated crackdowns against online pornography, calling it unhealthy and harmful.

But many Chinese-language pornography sites and some foreign-language pornography sites were accessible Friday and reports said they were apparently unblocked earlier this week. Other previously blocked sites now available included Voice of America, video-sharing site Vimeo and URL shortening site bit.ly.

China's message boards, where many of the country's 400 million-plus Internet users trade information and gossip, were surprisingly quiet about the newly unblocked sites. However, at least one posting on the topic could not be opened, indicating it was deleted by the site administrators or government censors.

It was not known whether there had been a change in policy or if the newly available sites were related to a technical problem. Calls to multiple offices at the Ministry of Industry and Information Technology rang unanswered Friday.

"I think it's totally just a glitch. These things have happened often before. (Censors) screw up and some site will suddenly become available for a day or two days and then be back to normal again. There's never any rhyme or reason to it," said Kaiser Kuo, a Beijing-based technology analyst. "It's almost certainly not deliberate policy."

The sites have become available amid a "sweep out pornography and prostitution" campaign in the Chinese capital of Beijing, which has resulted in the closure of several nightclubs and karaoke parlors.

___

Associated Press researcher Xi Yue contributed to this report.