Bitcoin traders using Blockchain, an iOS-compatible Bitcoin wallet application, met with a nasty surprise yesterday when Apple booted the app out of its App Store due to an “unresolved issue.” Blockchain isn’t the first Bitcoin transfer application to have met with resistance from Cupertino, and its removal seems to further suggest that the App Store is no place for the controversial virtual currency.

At the time of its removal, Blockchain was the world’s most popular Bitcoin app, allowing its 120,000 users to send and receive “bitcoins” – a virtual currency which has seen an unprecedented boom in value over the past year – using an iOS device. It’s no surprise to hear that while being the world’s most popular Bitcoin app, Blockchain was also the only iOS application that allowed Apple users to make mobile transactions using the currency.

However, in an email sent to Nicolas Cary, chief executive officer of Blockchain (which reached us from WIRED), Apple explained that the application has been “removed from the App Store due to an unresolved issue.” Curiously, the Cupertino, Calif. company didn’t go on to outline what, exactly, the issue at hand concerns.

Last year, a couple of similar apps – BitPak and Coinbase – were removed from the App Store, too. Bitcoin’s controversy partly surrounds its past association with the infamous Silk Road, and this also isn’t helped by its hazy classification as a legitimate currency. However, for Cary, Blockchain’s removal is less about Bitcoin and more about Apple’s long rumored interest in entering the mobile payments industry.

He said:

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.

Either way, folks looking to send and receive bitcoins using a native iOS application seem to have lost their last option. Perhaps we’ll see alternatives – or even Blockchain itself – appear in the Cydia Store. We’ll keep you updated with further information as we receive it.

In the meantime, see: Yahoo Releases iOS Editions Of Its Popular Bingo, Poker And Pool Online Games, Look, Ma, No PINs! BBM For iOS Now Lets You Easily Find Friends To Chat With, and Finally, The Long-Awaited Final Fantasy VI For iOS Is Out Now In The App Store.