US tech giant Meta's microblogging app Threads has topped 100 million registered users. The Twitter rival was released just five days ago.

Meta Platforms CEO Mark Zuckerberg announced the milestone in a Threads post on Monday. He said he was surprised at how quickly people were signing up and that growth was due to "mostly organic demand."

Meta released Threads last Wednesday. It was immediately available in over 100 countries, including Japan.

US media reports say the app reached 100 million users faster than any other platform in history, beating out ChatGPT which hit the mark in two months.

Video-sharing app TikTok took nine months to reach the milestone, while Meta's own Instagram took more than two years.

Twitter has suggested it will take legal action over Threads, which is similar in function and appearance to its platform. It claims Meta is unlawfully using trade secrets and intellectual property to develop the app.