Amazon has upped the stakes in its attack on Apple's iTunes. In a move intended to boost the company's audio download offerings, Amazon is to acquire digital audio books provider Audible.com for $300 million (£150m).

Amazon has been steadily building its digital music store to compete with Apple's iTunes. In January it gained a significant advantage over Apple when it became the only service to sell music from all four major record labels without copy protection, after signing up Sony BMG.

Apple no more?

But that's not the end of the story. Since 2003, Audible has maintained an exclusive agreement with Apple whereby it offers over 20,000 audiobooks for sale and download to iPod and iPhone owners via the iTunes Store.

Now that Amazon has acquired the company, speculation is rife that the Apple deal is over. It's thought that Audible's audiobooks will now be available only on Amazon's own MP3 download store.

"Audible.com offers the best customer experience, the widest content selection and the broadest device compatibility in the industry," said Steve Kessel, Amazon.com's senior vice president for worldwide digital media. "Working together, we can introduce more innovations and bring this format to an even wider audience."

Amazon has quickly grown from being an online bookseller to a provider of practically any product you might desire. The deal between Audible.com and Amazon is expected to be finalised by the second quarter of 2008.