Twitter has listed a new subscription service on app stores, in an indication that the social media giant is preparing to trial the offering soon.

"Twitter Blue" is listed as an in-app purchase, priced at £2.49 in the UK and $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.

It previously said it was working on special features for paid subscribers.

The firm wouldn't comment directly on the listing but highlighted to the BBC that it had previously announced plans to diversify its revenue sources.

Although "Twitter Blue" is now listed on app stores, it isn't yet fully enabled for users.

The BBC understands that pilot offerings of the subscription service are likely to start soon although it is unclear which countries it will be available in first.

According to technology blogger Jane Manchun Wong, who claims to be the first paying user of the service, it includes an "undo tweet" feature as well as a "reader mode" to make reading long threads easier. But Twitter has declined to confirm her claims.

The social media giant told the BBC that increasing "revenue durability" is the company's top objective.

The firm also plans to continue developing and experimenting with other ways to diversify its revenues beyond advertising this year and further ahead.

These plans could also include subscription services and other ways to offer individuals and businesses access to special features on the platform.

Twitter has also made clear that it will continue to focus on growing its advertising business.

Last month, the company launched a new "tip jar" feature that allowed people to send money to others on the social network.

Twitter said the feature was "an easy way to support the incredible voices that make up the conversation".

To begin with, only a select group of people can receive tips - a group Twitter said was made up of "creators", journalists, experts, and non-profits.

The function adds a small icon to a user's profile - on mobile devices only for now - with a drop-down menu for other payment providers such as PayPal, Venmo, or the Cash App, the latter two of which are popular in the United States.

But the announcement was not without controversy. Because the payment is made through those external systems, some Twitter users noticed that tipping a PayPal account lets the recipient know the postal address of the tip sender.

In other cases, the recipient's email address could be seen, whether or not any money was sent.

Reporting by Peter Hoskins.

Facebook and Twitter's chief executives were asked during a US Senate hearing in November if there was evidence of their platforms being addictive.