Twitter has threatened to sue Meta over its fast-growing rival Threads app, alleging that it stole trade secrets.

The Instagram and Facebook owner, which launched Threads on Wednesday, appeared to deny that former Twitter employees worked on the creation of the app and used insider knowledge.

Meta chief executive Mark Zuckerberg said more than 30 million people have signed up to use his rival messaging app in the first 24 hours since its launch.

However, a lawyer for Twitter, Alex Spiro, accused Meta of engaging in “systemic, wilful, and unlawful misappropriation of Twitter’s trade secrets and other intellectual property”.

The letter, which was first reported by Semafor, accused Meta of hiring “dozens” of former Twitter employees who “have access to Twitter’s trade secrets and other highly confidential information”.

In a tweet referencing the letter on Thursday evening, Twitter owner Elon Musk said: “Competition is fine, cheating is not.”

On Threads, Meta communications director Andy Stone posted in relation to the report: “No one on the Threads engineering team is a former Twitter employee — that’s just not a thing.”

US copyright law does not cover ideas so Twitter will need to prove that intellectual property has been stolen if the dispute is taken to court.

The Threads platform is freely available in 100 countries but it is not yet available in the EU due to regulatory concerns.

Linked to Instagram, it allows users to post up to 500 characters of text and up to five minutes of video and links, as well as pictures.

Many users have publicly expressed frustrations with Twitter since Mr Musk took over, partly linked to political views and erratic behaviour, as well as efforts to push more users towards its paid-for Twitter Blue service.

The new app is the latest chapter in the rivalry between Mr Zuckerberg and Mr Musk, who bought Twitter in October.

Last month, the pair – two of the world’s most high-profile billionaires – agreed to take each other on in a cage fight in an exchange that went viral on social media.

Meta and Twitter have been contacted for comment.