Online retailer Amazon.com Inc has signed on Warner Music Group Corp to its music download service, the latest major record label to join the competitor to Apple Inc's industry-leading iTunes store.

Warner Music songs were available as of Thursday on the Amazon MP3 service, which lets users purchase the tunes and download them to Apple's popular iPod or many other digital music players.

The companies said they will also offer exclusive tracks and special album bundles from Warner, the world's No. 3 music company, whose artists include Linkin Park and Red Hot Chili Peppers.

Amazon MP3 launched in September after reaching deals with music labels Universal Music Group, part of Vivendi , and EMI. The remaining major recording group, Sony BMG Music Entertainment, has yet to offer its songs for the service.

It has priced about one-third of its nearly 3 million songs at 89 cents each, below the standard iTunes price of 99 cents. The retailer recently began allowing customers to purchase songs by using regular Amazon.com gift cards.

Unlike Apple's store, Amazon's shop sells all of its songs without digital rights protection, allowing them to be played on a variety of devices in addition to the iPod.

Customers "can feel confident" their songs will play on whatever music device they buy in 2008, said Pete Baltaxe, Amazon's director of digital music.

"We're very pleased with where we are," Baltaxe said of customer adoption of the music service, though he would not provide data on downloads to date or site traffic.

U.S. album sales were down 14 percent in late November from a year earlier, according to Nielsen SoundScan data, as a growing number of fans buy individual songs online or use free file-sharing.

Digital music revenue has been growing in the double-digit percentages, but the total take is not enough to make up for the shortfall in compact disc sales.

Warner Music shares rose 10 cents to $6.07 on the New York Stock Exchange, while Amazon shares jumped $1.61 to $94.46 on Nasdaq.