Apple was dealt a blow in Europe on Wednesday when Norway’s powerful consumer ombudsman ruled that its iTunes online music store was illegal because it did not allow downloaded songs to be played on rival technology companies’ devices.

The decision is the first time any jurisdiction has concluded iTunes breaks its consumer protection laws and could prompt other European countries to review the situation.

The ombudsman has set a deadline of October 1 for the Apple to make its codes available to other technology companies so that it abides by Norwegian law. If it fails to do so, it will be taken to court, fined and eventually closed down.

Apple, whose iTunes dominates the legal download market, has its proprietory system Fairplay. Songs and tunes downloaded through iTunes are designed to work with Apple’s MP3 player iPod, but cannot be played on rival devices.

Torgeir Waterhouse, senior adviser to the Norwegian Consumer Council, who originally launched the complaint, told the Financial Times he was in negotiations with pan-European consumer groups to present a unified position on iTunes’ legality.

Sweden and Finland have already backed Norway’s stance, but have yet to take action, and Mr Waterhouse said the campaign was joined on Wednesday by Germany and France.

“We are satisfied the Federation of German Consumer Organisations and the French UFC Que Choisir are addressing this important issue. It means that iTunes is now being told by more than 100m European consumers to offer them a fair deal,” he said.

Apple signalled that it would fight efforts in Norway and elsewhere in Europe to prise open the iTunes service, though it struck a more conciliatory tone than early last year when it attacked a proposed French law as “state-sponsored piracy”.

“Apple is aware of the concerns we’ve heard from several agencies in Europe, and we’re looking forward to resolving these issues as quickly as possible,” it said in a statement. “Apple hopes that European governments will encourage a competitive environment that lets innovation thrive, protects intellectual property and allows consumers to decide which products are successful.”

The development comes as competition in the multi-billion dollar global market for digital music is intensifying.

Nokia, the world’s largest mobile phone maker, has set up a rival to iTunes, while Microsoft, the US technology company, has also launched its own digital music player called Zune to compete with the iPod.

However, the lack of interoperability has been blamed by some consumers and technology companies for hampering the growth of the legal digital music download market.

Record companies insist that the issue of interoperability is one for technology companies, and stress the importance of digital rights management in order to prevent piracy.

The IFPI, which represents record groups around the world, said that it “thoroughly supported interoperability, but wanted a market solution rather than one imposed by authorities”.