Napster on Tuesday opened the world's biggest MP3 download store with more than 6 million songs in a direct challenge to Apple's iTunes store.

The new Web-based music store will have digital songs from all major music labels as well as thousands of independent labels. The MP3-format songs will be compatible with the majority of digital media devices and mobile phones including Apple's popular iPod as well as its iPhone.

Before now Napster has focused on selling monthly streaming music subscription packages but has struggled to win over the majority of fans who want to be able to transfer songs they like on to a portable device such as the market-leading iPod.

The new Napster service tries to take on Apple's dominance in digital music by offering fans more songs without copy protection or digital rights management (DRM). Most of the six million songs on the iTunes Music store are available with Fairplay DRM, which prevents the songs from being played on most portable players other than the iPod.

"We're now moving from under the DRM cloud," said Chris Gorog, Napster chief executive. "Now consumers can use Napster with any device," he added.

Most songs on the service will be available for 99 cents each and $9.95 an album.

Though Napster will be hoping to take on iTunes it will try to do so by being compatible with Apple's service. According to executives, MP3 songs bought on the Napster Web-based service will be automatically synched into a user's existing iTunes music library if they use that library.

"We believe ultimately that consumers will be moving to an unlimited music model," said Gorog.