Search giant Yahoo has asked a US court to dismiss a law suit over allegations that the company contributed to the torture of Chinese dissidents.

The first-of-its-kind case was filed in San Francisco earlier this year under the Alien Tort Claims Act and the Torture Victims Protection Act, despite the fact that the related events took place in China.

Pro-democracy activists Shi Tao and Wang Xiaoning were jailed in separate instances after Yahoo provided Chinese authorities with access to their email and message board accounts. Both men allege that they were tortured after their arrest.

On Monday Yahoo's lawyers filed a motion arguing that the US legal system holds no jurisdiction over China's treatment of its citizens.

'Free speech rights as we understand them in the United States are not the law in China,' said Daniel Petrocelli, attorney for Yahoo.

'No matter how strenuous our disagreement, every sovereign nation has a right to regulate within its borders.'

The case will re-open debate over the responsibilities of search engines with regards to the user information they store. In most countries there is a legal obligation for web companies to make personal information available to the state in certain circumstances, but many users remain unaware of this fact.

'Web sites will offer the opportunity to read up on privacy policy, but few of us ever do,' said Newcastle University surveillance expert Dr David Murakami-Wood.

'Personally, I believe Yahoo is behaving appallingly in China.

'It is ethically inconsistent to think that rights only apply in countries where they are mandated by law,' said Murakami-Wood.

Earlier this year rival search engine Google attempted to appease privacy watchdogs by altering its policies. Personal information files will now automatically delete themselves from a user's computer after two years, provided no Google site is visited during this period.