Chinese authorities have released from jail dissident poet Shi Tao who was convicted based on information provided by US Internet giant Yahoo!, a rights group said Sunday.

Shi was released 15 months before the end of his 10-year sentence for leaking state secrets after he sent an email overseas containing information on a crackdown on democracy advocates, PEN International said.

Information supplied by Yahoo! was used to help convict him, said a statement from the London-based group, which promotes freedom of expression.

The reason for Shi's early release was not given.

Pen International quoted Shi as saying that he was treated "relatively well" in prison and had continued to write.

Shi, who also worked as a freelance journalist contributing to a newspaper in the central city of Changsha, could not be immediately reached for comment.

Another Chinese dissident, Wang Xiaoning, who was also convicted based on evidence provided by Yahoo! was released from prison last year after serving a 10-year term for subversion.

Yahoo! executives who previously testified before the US Congress said they were legally obliged to divulge information about their users to the Chinese government and that they were unaware it would be used to convict dissidents.

But Yahoo! later apologised and in 2007 paid compensation to Wang's wife after the World Organization for Human Rights lodged a lawsuit.

Wang was jailed for distributing essays that advocated democratic reform and criticised China's one-party Communist rule using his Yahoo! email account.

Yahoo's China arm shut down its email service for users last month, illustrating the brand's diminishing profile in the country.

China Yahoo! has been operated by Alibaba since 2005, as part of a strategic partnership with Yahoo! which included the US firm buying a stake in the Chinese e-commerce giant.

Alibaba is now preparing for a massive stock offer, while also buying back the stake from Yahoo.