Apple has removed the world's most popular bitcoin wallet from its App Store.

Late Wednesday, the tech giant yanked the Blockchain app from the popular mobile app marketplace and did not provide a specific reason, says Nicolas Cary, the CEO of Blockchain. The app is currently used by about 120,000 people to send and receive the world's most popular digital currency. Blockchain users can still run the app on their iPhones and Macs, but they will no longer be able to get software updates via Apple. There are more than 1 million Blockchain users worldwide.

Apple could not be immediately reached for comment, but Cary forwarded WIRED a copy of the email he received from Apple. It says the app had been "removed from the App Store due to an unresolved issue." Whatever the particulars of the removal, it's yet another bump in the road as bitcoin struggles to gain mainstream acceptance.

Before it got pulled, Blockchain had been the only bitcoin wallet app available to Apple users, Cary says.

Last year, a wallet called BitPak shut down operations after being turfed from the App Store, and in November, Apple bumped another popular bitcoin wallet, called Coinbase. It had survived less than a month in Apple land. The Blockchain was released in the App store in April 2012. Apple had previously removed the Blockchain app too, but it was later re-accepted, Cary says.

Some believe that Apple may be dumping bitcoin wallets because of the emerging, somewhat confusing international regulations surrounding bitcoin. But like others, Blockchain's Cary argues that his app was pulled because Apple sees bitcoin as a potential competitor. "I think that Apple is positioning itself to take on mobile payments in a way they haven't described to the public and they're being anti-competitive."

In contrast, bitcoin is still welcome on Android. Both the Blockchain and Coinbase apps are available on Google Play. And Google is reportedly looking into ways of working with the digital currency. "We're totally cool with Google," says Cary.