Civil rights group Amnesty International launched a campaign against Internet censorship on Sunday, accusing multinational companies of complicity in aiding countries such as China to hampering free access to online information.

In the British newspaper The Observer, Amnesty U.K. director Kate Allen targeted Yahoo, Microsoft and Google for complying with the censorship rules of the Chinese government. She also criticized Cisco Systems and Sun Microsystems for supplying hardware that enables filtering and monitoring of Web traffic.

"The Internet is big business, but in the search for profits some companies have disregarded their own principles and those on which the internet was founded: free access to information," Allen wrote on the 45th anniversary of the publication of an article leading to Amnesty International's creation.

Technology companies have defended their decision to operate in China, saying they must comply with local laws if they want to do business. Critics have assailed the defense, arguing tech companies have equipped Chinese authorities with advanced tools to repress information.

A report by the OpenNet Initiative study released in April found that China has a "sophisticated" Internet filtering system that encompasses Web pages, e-mail messages, blogs, online discussion forums and university bulletin-board systems. The group is a partnership composed of University of Toronto, Harvard Law School and the University of Cambridge.

Allen wrote that Amnesty has documented Internet censorship in Iran, Turkmenistan, Tunisia, Israel, the Maldives and Vietnam.

Amnesty also started a Web site, irrepressible.info, to support the drive, which will include lobbying governments to release those jailed for activities related to Internet use.