US music companies have gone back to court to appeal against a ruling which cleared peer-to-peer (P2P) sites Grokster and StreamCast of copyright infringement.

In recent months the Recording Industry Association of America (RIAA) has turned its attention to individual users, with hundreds of people expected to face lawsuits over the next few weeks.

But yesterday the entertainment companies, including AOL Time Warner and Sony, plus some smaller independent labels, filed court papers with the Ninth US Circuit Court of Appeals in San Francisco.

They want the court to re-examine the arguments against the P2P sites and to make them accountable for infringement.

In his original ruling in April, US District Judge Stephen Wilson said P2P sites such as Grokster and StreamCast could not be held responsible for what individuals did with the technology.

"Grokster and StreamCast are not significantly different from companies that sell home video recorders or copy machines, both of which can be, and are, used to infringe copyrights," he said.

The ruling came as a huge blow to the music industry's battle to stamp out what it claims is the illegal downloading of music and movie files.

Cary Sherman, president of the RIAA, said: "[The court's decision] was wrong.

"These are businesses that were built for the exclusive reason of illegally exchanging copyrighted works, and they make money hand over fist from it. The Court of Appeals should hold them accountable."

But Wayne Rosso, president of Grokster, described the application to overturn Wilson's decision as an "exercise in futility".

He said AOL Time Warner, Sony and other entertainment companies were bringing no new arguments to the table.

Rosso said the appeal will be heard within the next few weeks, but added that he was not concerned that the outcome would be any different from the original ruling.

"This is just another act of desperation. They don't have the law on their side and they are offering the same arguments verbatim. We will prevail," he said.