Amnesty International said American companies are helping China monitor the Internet by selling them blocking software and the like - boosting China's ability to muzzle discussion online.

The human rights group is also demanding the release of 33 people imprisoned for online subversion and says such detainees are emerging as a new category of Chinese 'prisoners of conscience.' The report is the first in which Amnesty identifies Internet users as a new class of dissident - alongside the religious, political and minority rights dissenters already targeted by China.

China's Communist Party has worked to squelch any role for the network as a forum for free speech. Blocks are placed on scores of Web sites belonging to foreign governments, news organizations and human rights groups - including Amnesty. Gambling and pornography Web sites are blocked, as well as any site the Chinese government considers extremist.

Thousands of Internet cafes closed after a deadly fire in Beijing have been allowed to reopen only after installing monitoring software. Police monitor e-mail accounts and Internet usage, and Amnesty says some 30,000 officers have been assigned to Internet duty.

Despite China's relative success at bringing the Internet to heel, the wealth that the new technology it is creating will eventually produce calls for greater protection of civil liberties, Amnesty said.

'As the importance of the Internet grows,' the report said, 'so too will the millions of users and the demands of those seeking justice and respect for human rights in China.'