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Amazon has unveiled a colour tablet computer called the Kindle Fire.

The $199 (£130) device will run a modified version of Google's Android operating system.

Until now, the company has limited itself to making black and white e-readers, designed for consuming books and magazines.

As well as targeting Apple's iPad, Amazon is likely to have its sights on rival bookseller US Barnes & Noble, which already has a colour tablet.

The Kindle Fire will enter a hugely competitive market, dominated by Apple's iPad.

Amazon will be hoping to leverage both the strength of the Kindle brand, built up over three generations of its popular e-book reader, and its ability to serve up content such as music and video.

In recent years, the company has begun offering downloadable music for sale, and also has a streaming video-on-demand service in the United States. Those, combined with its mobile application store, give it a more sophisticated content "ecosystem" than most of its rivals.

"It's the price and the backup services that make it really exciting," said Will Findlater, editor of Stuff magazine.

"Content is the big differentiator. It's what every other platform has been lacking, except the iPad."

Amazon's decision to opt for a 7" screen, as opposed to the larger 10" displays favoured by many rival manufacturers was a cause for concern for Ovum analyst Adam Leach.

"This screen size has undoubtedly helped them achieve a lower price point for the device but so far this form factor has not been popular with consumers, we shall see if this is related to other aspects of those devices other than its screen size. "

Digital content has already proved itself to be a money-spinner for Amazon.

Although the company has never released official sales figures for the Kindle, it did state - in December 2010 - that it was now selling more electronic copies of books than paper copies.

Its US rival, Barnes & Noble, has also enjoyed success with its Nook devices.

In October 2010, the company unveiled the Nook Color, which also runs a version of Android, albeit with lower hardware specs than many fully featured tablets.

While the Nook Color is largely focused on book and magazine reading, some users have managed to unlock its wider functionality and install third-party apps.

The Kindle Fire's $199 (£130) price tag undercuts the Nook Color by $50 (£30) and is significantly cheaper than more powerful tablets from Apple, Samsung, Motorola and others.

It is due to go on sale on 15 November in the US, although global release dates are currently unavailable.

Alongside the Kindle Fire, Amazon also announced a refresh of its Kindle e-readers.

The entry level device has had its keyboard removed and will now sell for $79, down from $99. Amazon UK announced that the new version would retail at £89.

A version with limited touchscreen capability, known as the Kindle Touch, will sell for $99. Only the US pricing has been announced so far.

"These are premium products at non premium prices," said Amazon chief executive Jeff Bezos. "We are going to sell millions of these."