A US federal court has dealt a blow to a music website offering sales of "pre-owned" digital music, ruling that it violates copyright law by making illegal reproductions.

The ruling released over the weekend by Judge Richard Sullivan came in a closely watched case in which Capitol Records sued the website ReDigi, which calls itself "the world's first pre-owned digital marketplace."

The ruling, which could have broad implications for resale of digital music, said ReDigi was not reselling products previously owned but was making unauthorized copies.

"It is simply impossible that the same 'material object' can be transferred over the Internet," the judge wrote in an 18-page decision.

"Because the reproduction right is necessarily implicated when a copyrighted work is embodied in a new material object, and because digital music files must be embodied in a new material object following their transfer over the Internet, the court determines that the embodiment of a digital music file on a new hard disk is a reproduction within the meaning of the Copyright Act."

Because of this, the judge said the so-called "first sale" doctrine which can be applied to books "does not protect ReDigi's distribution of Capitol's copyrighted works."

Capitol Records, a unit of Universal Music Group, owns the rights to songs including Frank Sinatra's "Come Fly With Me" and The Beatles' "Yellow Submarine."

There was no immediate comment on the decision Monday from ReDigi.

The judge asked the parties to submit statements on an injunction and damages in the case.