A preliminary injunction requested by Amazon was issued by Judge Patricia Campbell-Smith, barring the Department of Defense from starting work on the contract known as JEDI, according to a summary of the ruling.

Details of the ruling were sealed for unspecified reasons.

Amazon has alleged it was shut out of the deal because of President Donald Trump's vendetta against the company and its chief executive Jeff Bezos.

It's seeking testimony from the president and other top officials on the reasons for awarding the $10 billion, 10-year US military cloud computing contract to Microsoft.

"We are disappointed in today's ruling and believe the actions taken in this litigation have unnecessarily delayed implementing DoD's modernization strategy and deprived our warfighters of a set of capabilities they urgently need," Department of Defense spokesman Lt Col Robert Carver said.

He added that the Pentagon remained confident in its decision to award the contract to Microsoft.

The Joint Enterprise Defense Infrastructure (JEDI) program will ultimately see all military branches sharing information in a cloud-based system boosted by artificial intelligence.

An earlier court filing by Amazon detailed alleged errors that ended with Microsoft being chosen over its Amazon Web Services (AWS) cloud computing division, part of the technology group led by Bezos.

Bezos, who also owns The Washington Post, is a frequent target of the US president, who claims the newspaper is biased against him.

- Microsoft confident -

Microsoft said it hoped to prevail after the merits of the case are heard in court.

"We have confidence in the Department of Defense, and we believe the facts will show they ran a detailed, thorough and fair process in determining the needs of the warfighter were best met by Microsoft," said Frank Shaw, the company's vice president of communications.

Amazon did not immediately respond to a request for comment.

Amazon was considered the lead contender to provide technology for JEDI, with AWS dominating the cloud computing arena and the company already providing classified servers for other government agencies including the CIA.

Amazon argued in court documents that the Pentagon's choice of Microsoft was mystifying if not for Trump's repeated "expressed determination to, in the words of the president himself, 'screw Amazon.'"

The protest filed in the US Court of Federal Claims urges that the rival JEDI bids be re-evaluated.

As a condition of the injunction, Amazon was directed to provide $42 million to the court that would be used to cover any costs or damages incurred if it is determined that the injunction was issued wrongly.