San Francisco  - Amazon.com posted an 18-per-cent boost in sales and a 24 per cent rise in profits as the online retail giant shrugged off the effects of the economic downturn.

The Seattle-based retailer said that it earned 177 million dollars in the first quarter, compared to 143 million dollars a year ago. Sales were up to 4.89 billion dollars compared to 4.13 billion dollars a year ago.

International sales went up 15 per cent from the first quarter of 2008 to 2.31 billion in the same period this year. The company said that figure would have been 28 per cent if it weren't for unfavorable currency exchange rates.

But the company said the strongest boost to its earnings came from sales of its new electronic book reader, the Kindle, which sold more than 300,000 units.

"We're grateful and excited that Kindle sales have exceeded our most optimistic expectations," Amazon founder and chief executive Jeff Bezos said.