Customers can buy tunes through Gbox at the same price charged by market leader iTunes - 99 cents (50 pence) a track.

Music fans can download tracks direct from Gbox or from the online retailer Amazon. However, only US customers can currently make use of the service.

Gbox will also benefit from a special advertising deal with Google.

The adverts, which will appear when a user searches for a particular term, such as the name of an artist, will link to the Gbox site.

However, the search engine giant will get standard advertising fees rather than a cut of sales under the arrangement.

Music online

The new service is offering downloads of Universal Music artists including Prince, 50 Cent and Johnny Cash without the customary copy protection technology known as DRM - digital rights management.

Most major recording studios insist music sellers use DRM technology on digital music formats to curb online piracy.

The new site also hopes to use social networking sites like MySpace to sell its music.

Gbox maker, Navio Systems, is providing users with software code which users can place on blogs, so they can set up a wish list of songs that they would like to be bought for them.

Universal Music Group chief executive Doug Morris said that the move would provide a "valuable insight" into the implications of selling music without rights management technology attached.

"We're committed to exploring new ways to expand the availability of our artists' music online, while offering consumers the most choice in how and where they purchase and enjoy our music," he said.

The launch of Gbox came on the same day that Wal-Mart's online music store began selling songs free of DRM technology, at 94 cents per tune.