American Express customers will be able to buy goods online at discounted rates by tweeting a designated hashtag from their Twitter account, thanks to a new service launched by the credit card operator yesterday.

The discount hashtags will be published on American Express's official Twitter account. Once a customer has registered their Twitter account with American Express, they can then tweet the hashtags to receive a discount.

After mentioning the hashtag on Twitter, the user will be sent a confirmation tweet by American Express. They must reply to this tweet to complete the transaction, and the product will be delivered within two days.

Products available through the scheme include Amazon's Kindle and Sony's Xbox 360 console.

The 'Amex Sync' service follows a similar scheme from American Express last year, which issued discounts for use in store.

"Based on the initial success of Amex Sync for offers, we know there is significant power in combining our assets with Twitter's platform to bring value to cardmembers and merchants," said Leslie Berland, senior vice president of digital partnerships and development at American Express.

"Now, we're leveraging our unique technology and closed-loop network to introduce a seamless solution that redefines what's possible in the world of social commerce."

Other recent examples of social commerce initiatives include an offer from Amazon.com, giving customers a $5 discount if they share the name of who was "at the top of their holiday gift list" on Facebook.

The purpose is these schemes is to use customers' own social networks to raise awareness of offers and discounts.