WhatsApp rival Kik Messenger has closed down its app amid a legal battle against the US Securities and Exchange Commission over its digital currency offering.

The chief executive of the popular online app confirmed it was to close the messaging side of the business to focus on battling the US authorities over its cryptocurrency in court.

Kik Messenger will close despite having millions of users who prefer it to rivals including Telegram and WhatsApp because it does not require users to provide a phone number or any other credentials to use the service.

The Canadian company first launched its cryptocurrency, called Kin, in 2017 as one of the highest-profile companies to participate in a wave of initial coin offerings, raising funds for digital projects that are typically less regulated than traditional investments.

Ted Livingston, the founder of the company, said: "While we are ready to take on the SEC in court, we underestimated the tactics they would employ. How they would take our quotes out of context to manipulate the public to view us as bad actors. How they would pressure exchanges not to list Kin. And how they would draw out a long and expensive process to drain our resources."