US media company Yahoo is facing a lawsuit accusing it of aiding and abetting human rights abuses in China by supplying information on dissidents that led to their imprisonment.

Last week, Yahoo and MSN China signed a code of conduct for their blogging operations that committed them to protecting the interests of the Chinese state.

The firms signed the self-discipline pact, under which they pledged to safeguard state and public interests.

The pact 'encourages' Internet firms to register the real names, addresses and other personal details of bloggers, and retain this information.

The firms also committed to delete any 'illegal or bad messages'.

Search engine Google has also been accused of collaborating with Chinese authorities. It freely admits to blocking politically sensitive items on its Chinese website.

The current lawsuit was filed in a federal court in San Francisco by the World Organization for Human Rights on behalf of the wife of Wang Xiaoning, a Yahoo user jailed in China for promoting democracy online.

The suit accuses Yahoo of helping Chinese officials track down her husband and of linking him to email and online comments.

Yahoo was referred to 10 times in the Chinese court verdict that declared Mr Wang guilty of incitement to subvert state power and sentenced him to 10 years in prison.

In response, Yahoo said the dissidents 'assumed the risk of harm when they chose to use Yahoo China email and group list services to engage in activity they knew violated Chinese law'.

Calling for the legal action to be dismissed it said: 'free speech rights as we understand them in the US are not the law in China, every sovereign nation has a right to regulate speech within its borders'.

Yahoo was previously criticised for passing on information to Chinese authorities about another of its users, who was sentenced for divulging state secrets.

The man had posted a Chinese government order, forbidding media organisations from marking the anniversary of the 1989 Tiananmen Square uprising.

International press freedom group Reporters Without Borders has condemned the conduct of companies such as Yahoo and Google in China.