Amazon's MP3 music download service, although touted as a success since its launch last year, has not impacted on Apple's iTunes customers, a recent study says.

Analysis by The NPD Group reveals that just 10% of all purchasers at Amazon MP3 are customers pinched from Apple's service, with the rest either switching from other stores or else are new to download music.

This is a "healthy indication that the digital music customer pool can expand into new consumer groups who have not yet joined the iTunes community", said an NPD analyst.

Amazon currently enjoys the fourth place spot among all US music sales but has just a tenth of the sales volume of iTunes.

Amazon's MP3 service, that offers DRM-free music from the four major music labels that can be played across all devices, has yet to launch outside of the States.