Facebook founder Mark Zuckerberg has said that an alleged contract and e-mails that a New York man claims entitle him to a 50% stake in the social networking site are "forgeries".

Paul Ceglia says that Mr Zuckerberg signed a contract in 2003 which gave Mr Ceglia half-ownership of Facebook.

In a court filing, Facebook and Mr Zuckerberg demand that Mr Ceglia turn over the alleged contract and e-mails.Lawyers representing Mr Ceglia disputed Facebook's claims.

In a filing made at the US District Court in Buffalo, Mr Zuckerberg said he provided web development services in 2003 for StreetFax, a business Mr Ceglia was trying to start at the time.

He said he signed a contract drafted by Mr Ceglia, a wood pellet salesman, which referred only to the work he did for StreetFax."Zuckerberg and Ceglia never discussed Facebook and they never signed a contract concerning Facebook," the filing said.

"The contract is a cut-and-paste job, the e-mails are complete fabrications, and this entire lawsuit is a fraud." Facebook and Mr Zuckerberg hope to use forensic testing to show that the documents are fakes.

Twins Cameron and Tyler Winklevoss also claimed that Mr Zuckerberg stole their website idea while they were all students at Harvard.

In 2008 they reached a settlement which gave them $20m in cash and $45m of stock valued at $36 a share.

They have since unsuccessfully tried to reopen their case against Facebook, claiming that the company concealed information and they should have received more shares.

Facebook is privately owned but estimates of its worth range between $50bn (£30bn) and $76.4bn (£46.7bn).