The Facebook CEO was asked for his opinion on the antitrust backlash the tech giant is facing.
Appearing on HBO's 'Axios', he said: "Well I certainly think that they have the unilateral control of what gets on the phones in terms of apps.
"I think it's probably about 50% of Americans who have smart phones, and a lot more people around the world. I think there are more than a billion Apple devices. So I do think that there are questions that people should be looking into about that control of the App Store and whether that is enabling as robust of a competitive dynamic."
By contrast, the billionaire entrepreneur was full of praise of the App Store's rival Google Play Store.
He added: "As a developer if you're not in the Google Play Store, at least you still have a way to get your app on people's devices. And that means that people aren't completely going to be shut out if they're doing something that Google doesn't prefer. I think that that's really important, that people have a way to create something and get it on devices if people want."