Online retail giant Amazon said Monday that sales of electronic books for the Kindle have overtaken hardcover book sales.

Amazon founder and chief executive Jeff Bezos also said the growth rate of sales for the Kindle has tripled since the company cut the e-reader's price from 259 dollars to 189 dollars a month ago.

"We've reached a tipping point with the new price of Kindle," Bezos said in a statement.

"In addition, even while our hardcover sales continue to grow, the Kindle format has now overtaken the hardcover format," he said.

"Amazon.com customers now purchase more Kindle books than hardcover books -- astonishing when you consider that we've been selling hardcover books for 15 years, and Kindle books for 33 months," Bezos said.

Amazon said that over the past three months, it has sold 143 Kindle books for every 100 hardcover books sold. Over the past month, Amazon has sold 180 Kindle books for every 100 hardcovers sold, it said

The figures do not include sales of paperbacks.

The Seattle-based online store also said it has sold three times as many Kindle books in the first half of 2010 as in the first half of 2009.

Amazon does not release sales figures for the Kindle but says it has been the company's bestselling item for two years.

Facing competition from Apple's new iPad tablet computer, Amazon dropped the price of its basic Kindle on June 21 to 189 dollars.

On July 1, Amazon unveiled a new large-screen version of its Kindle and cut the price to 379 dollars from 489 dollars.

Apple's cheapest iPad, the Kindle's chief rival, costs 499 dollars and features a color e-reader compared with the black-and-white Kindle, which is devoted exclusively to digital books.