The Amazon Flexible Payments Service (FPS) is a package of Web services APIs that allow the movement of money between any two entities, humans or computers using Amazon's existing payment infrastructure.

Amazon says the system, which is in limited beta phase, has been designed "from the ground up" specifically for use by developers of Web sites and applications. The FPS service can be set up to send and receive money using credit cards, bank accounts or Amazon Payments balance transfers.

Developers are able to set up an unlimited number of payment instructions, says Amazon, and can create both simple and complex payments instructions. The technology can also be used to build marketplace applications that enable the movement of money between two third parties.

The system also enables Amazon customers to use the same payment instruments that they use for purchases on Amazon sites to pay for purchases on sites featuring the FPS application, without having to re-enter their information.

There are no minimum fees and no startup charges to use FPS, says Amazon, and all pricing is per-transaction based on the transaction size and the payment method. On its Web service blog, Amazon says the first applications incorporating FPS will be available "very soon".

The launch of the beta follows heated speculation that Amazon is gearing up to launch an electronic payments service to rival Paypal and Google Checkout.

However there are questions over whether eBay will allow applications using the Amazon payment service to be used on its auction site, especially as the online flea market promptly banned the Google Checkout Web payments service shortly after it was launched last year.

EBay said in April that it will fight a class action lawsuit in California over allegations that its PayPal subsidiary has sought to improperly monopolise the forms of payment that sellers can use on the auction site.