Apple has been found guilty of conspiring with book publishers to raise ebook prices, in one of the biggest anti-trust lawsuits ever brought by US federal authorities.

US district judge Denise Cote ruled on Wednesday that the company played a "central role" in a conspiracy with the biggest book publishers in the US to fix prices in violation of antitrust law.

Executives from the companies would meet in the private dining rooms of upscale New York restaurants to bemoan the low prices charged by the ebooks market leader Amazon, and what they could do about it, Cote said in her ruling.

Cote ruled that that damages would be determined at a new hearing. Apple continued to deny on Wednesday that it had done anything wrong, and said it planned an appeal.

The ruling was not unexpected, as Cote had earlier suggested that Apple's defense would fail, and the publishers – Hachette Book Group Inc, Macmillan, HarperCollins Publishers LLC, Penguin Group and Simon & Schuster – settled with the Department of Justice ahead of the trial. With Random House, these six firms are the largest publishers of trade books in the United States.

In a statement after the ruling, Apple said:

Apple did not conspire to fix ebook pricing and we will continue to fight against these false accusations. When we introduced the iBookstore in 2010, we gave customers more choice, injecting much needed innovation and competition into the market, breaking Amazon's monopolistic grip on the publishing industry. We've done nothing wrong and we will appeal the judge's decision.