Facebook owner Meta's new Threads app, meant to rival Twitter, will not be available in the European Union when it launches Thursday because of regulatory concerns, a source close to the company said.

The app is seen as the biggest challenge yet to Twitter since the takeover by Elon Musk sent the social media platform, hugely popular with politicians and celebrities, into chaos.

A source close to Meta said Wednesday that the tech giant was holding back from a Threads release in the EU's 27 countries as it sought clarity on the bloc's Digital Markets Act that will come into full force next year.

The DMA is a landmark law that sets strict rules for the internet's biggest companies in Europe.

One of those regulations prohibits platforms from sharing data across different services. It also restricts companies directing platform users to their own products.

The description of Threads on app stores in the United States indicated that a user's personal data, including contact and geolocation information, will be collected and used for advertising purposes.

Meta has already run afoul of EU rules for its attempts to use data from WhatsApp to strengthen Instagram and Facebook, something European regulators forbade it from doing.

A spokesman for Ireland's Data Protection Commission told the Irish Independent that Meta confirmed that it would not be releasing the app in Europe "at this point".

Ireland is home to Meta's EU headquarters, and the national regulator is in charge of oversight of the company in Europe.

Contacted by AFP, Meta did not immediately comment.

Meta was one of seven companies, including Amazon and Apple, that informed the EU on Tuesday that they meet the threshold to come under the new rules when they come into force next year.