Last.fm claims to have become the fastest growing online music network in the US, with a unique listener increase of 92 per cent since launching four weeks ago.

The social networking music site said that it has more than 21 million active users worldwide every month.

Martin Stiksel, co-founder of the site, said: "We have created a new model that works for everyone - listeners, artists and copyright holders - and the user response proves that it is working.

"Free is the future, and this is signalled not only by the industry's growing acceptance of what we're doing, but more importantly by the incredibly fast increase of users accessing music on Last.fm since we launched free-on-demand."

Last.fm claimed to have become the first music site to offer free, global on-demand access to the largest licensed catalogue of music.

The firm has partnerships with all four major record labels - Universal Music Group, Sony/BMG, Warner and EMI - as well as CD Baby, IODA, the Orchard, Naxos and more than 150,000 independent labels and artists.

This is at a time when licensing disputes have put other music sites, such as Pandora, out of action outside the US.

Last.fm's free-on-demand service is presently available in the US, UK and Germany, without registration or the download of any software, and is scheduled to roll out globally in the coming months.