Amazon.com has updated its Kindle application allowing audio and video clips to be embedded in electronic books served up on Apple's popular iPad, iPhone, or iPod touch gadgets.

"We are excited to add this functionality to Kindle for iPad and Kindle for iPhone and iPod touch," Amazon Kindle director Dorothy Nicholls said in a release.

"We look forward to seeing what authors and publishers create for Kindle customers using the new functionality of the Kindle apps."

Slightly more than a half-dozen e-books taking advantage of the new technology were available at amazon.com/kindleaudiovideo on Monday. Titles included "Rick Steves' London 2010" and "We Cannot Fail" by Terry Golway.

"In the new Kindle Edition with audio/video of Rick Steves' London, the embedded walking tours allow customers to listen to Rick as they explore the sites of London," said Avalon Travel publisher Bill Newlin.

"Rick's narration adds depth to the reader's experience, while listeners can follow the routes more easily with the text."

A digital version of "Rose's Heavenly Cakes" featured video tips for baking recipes.

"Innovations like these represent the advantages that digital can offer," said Peter Balis, director of digital content sales at Wiley.

"Advancing our content in this manner is important for our authors and our readers and it will raise the bar on what digital reading can offer for years to come."

Amazon on Monday also released a free Kindle application in the United States for smartphones based on Android software backed by Apple rival Google.

Kindle for Android was available at the online Android Market.

Synching technology used by Amazon lets people read Kindle books on an array of devices, switching as they wish.

"Our customers tell us they love the convenience of having their Kindle library with them everywhere and their reading synchronized across multiple devices," Nicholls said.

Last week, Amazon and US bookstore giant Barnes & Noble cut the prices of their electronic book readers in the face of Apple's iPad momentum in the fledgling market.

Amazon dropped the price of its Kindle e-reader to 189 dollars from 259 dollars.

The cheapest iPad, a multi-purpose tablet computer that features a color e-reader compared with the black-and-white "e-ink" Kindle devoted exclusively to digital books, costs 499 dollars.

Barnes & Noble lowered the price of the Nook with 3G and Wi-Fi connectivity to 199 dollars from 259 dollars.

Barnes & Noble also said it was introducing a Wi-Fi only version of the Nook for 149 dollars. Kindle has 3G wireless connectivity to allow users to quickly download digital books.

Barnes & Noble's chief bookstore competitor, Borders, also offers an e-reader, the Kobo, for 150 dollars.

Apple has sold more than two million iPads since the touch-screen tablet computer went on sale in the United States in early April and in nine other countries late last month.

The culture-changing California firm reported on Monday that it sold 1.7 million of its new-generation iPhone 4 in the three days after it hit the market Thursday.