Micro-blogging service Twitter has unveiled a beta version of its much-talked about 'verified accounts' service.

The service, which is currently available only to "public officials, public agencies, famous artists, athletes, and other well known individuals at risk of impersonation", will see a speacial seal bestowed on certain accounts to indicate to Twitter users that it is real.

The move follows a law-suit bought against Twitter by the manager of US baseball team the St Louis Cardinals, Tony La Russa. Russa says Twitter doesn't do anough to stop impersonators on the service. However Twitter called Russa's lawsuit "an unnecessary waste of judicial resources bordering on frivolous".

"We hope to verify more accounts in the future but due to the resources required, verification will begin only with a small set," Twitter added in a blog.

"When we do start testing Account Verification, we will be sure to provide ample methods for feedback. Initially, verification will not be tested with businesses. However, we do see an opportunity in that arena so we'll keep you posted when we have something to share."