Apple Inc.’s clash with Epic Games is being followed with “great interest” amid concerns over a duopoly in the app store market, Germany’s antitrust chief Andreas Mundt said on Wednesday.

The case highlights that app stores pose competition issues that regulators are only beginning to recognize, Mundt told reporters at the annual press conference of the Federal Cartel Office. While his authority hasn’t opened a probe, he said the issue isn’t beyond its jurisdiction.

“One thing is clear: app stores are an interesting biotope, simply because there are only two of them globally,” said Mundt, referring to Apple’s App Store and Google Play. “Every developer on this planet who produces an app needs to pass through their gates -- that’s indeed interesting, to put it cautiously.”

Apple is under investigation by the European Union, which is reviewing whether the company unfairly forces software makers to use its own in-app payment system that typically takes a 30 per cent cut of subscription fees. In the U.S., the iPhone maker is embroiled in a bitter legal fight over the same issue with Epic, the maker of the popular Fortnite video game.

Apple didn’t immediately respond to a request for comment.

The Cupertino, California-based technology giant had recently threatened to pull Epic’s developer account after the game maker added an option for Fortnite players to avoid the 30 per cent cut that Apple takes through its App Store. Last week, Apple terminated Epic’s account, making it impossible to update the Fortnite app in its store.