Did Albert Einstein say "Compound Interest is the most powerful force in the Universe."

The other day I was playing Civilization IV when I heard the quote "Compound interest is the most powerful force in the universe." it was cited that this quote came from Albert Einstein. This sounded like a quote more likely to have come from a banker or politician than a famous physicist. I decided to do some investigating to see whether or not Mr Einstein ever actually said this.

After a quick trawl on the net it was apparent that this was a commonly held belief with over 61,500 results for "Einstein compound interest" alone. However, I could not find one reference to Albert himself saying it - with the earliest reference to the phrase being in New York Times blurb from 1983.

Some people also attribute this saying to Mark Twain however, it is not mentioned once in any of his writings.

Can anyone out there give me an insight into where this saying originated?