Micro-blogging site Twitter has listed a new subscription-based service "Twitter Blue" on App Store, in an indication that the company is preparing to trial the offering soon.

"Twitter Blue" is listed as an in-app purchase, priced at 2.49 pound in the UK and USD 2.99 in the US.  Twitter has given no further details and declined to confirm online claims that the service could allow users to "undo" tweets.