Steve Ballmer, Microsoft's chief executive, vowed to "kill" Google, according to documents presented in the legal battle between the internet rivals.

The allegations, contained in documentary evidence lodged with a Washington state court, are the latest salvos in a showdown triggered by Google’s hiring of a former Microsoft executive, Kai Fu-Lee.

Mr Lee was recruited to oversee Google's planned research and development centre in China. He started at Google in July, the day after he resigned from Microsoft.

The tug-of-war over Mr Lee, known for his work on computer recognition of language, has now hinted at the full extent of the animosity between the two companies.

Mr Ballmer’s tirade, which included obscenities as well as the threat, was made last November, according to allegations in sworn evidence from a former Microsoft engineer, Mark Lucovsky.

Mr Lucovsky said he had met Microsoft’s chief executive ten months ago to discuss his decision to leave the company after six years.

According to the document, after learning that Mr Lucovsky was taking a job at Google, Mr Ballmer picked up his chair and hurled it across his office. Mr Ballmer then said of the Google chief executive, Eric Schmidt: "I’m going to f****** bury that guy, I have done it before, and I will do it again ... I’m going to f****** kill Google."

Before joining Google, Mr Schmidt was at Sun Microsystems and Novell, two Microsoft rivals.

After the release of the court documents, Mr Ballmer described Mr Lucovsky’s recollection as a "gross exaggeration".

He said: "Mark’s decision to leave was disappointing and I urged him strongly to change his mind. But his characterisation of that meeting is not accurate."

Microsoft is seeking to prevent Mr Lee from leading Google’s China expansion, maintaining that those duties would violate the terms of a non-competition agreement he signed as part of his employment contract.

Google has depicted Microsoft’s case as a form of intimidation designed to thwart a fast-growing rival that has emerged as a formidable threat to the software maker.

The declaration by Mr Lucovsky is just one piece of evidence that Google has filed in an attempt to prove that Microsoft has launched a vendetta against it.

Microsoft won the first round in the case in late July when King County Superior Court Judge Steven Gonzalez issued an order temporarily barring Mr Lee from working at Google.

The court case resumes tomorrow when Microsoft will ask the judge to extend the order against Mr Lee and Google until the case goes to trial in January.

Microsoft is trying to demonstrate that Google wanted Mr Lee largely because he knows intimate details about Microsoft’s strategy for expanding in China and for the booming search engine market.

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