Clues suggest that Apple iOS 7 could have sharp-cornered square app icons, as part of the biggest visual shake-up since Apple's mobile operating system first launched.

Developers told AppleInsider that the portal where they upload their apps has started displaying the icons as sharp squares instead of the familiar rounded squares all iOS users are used to. Previously app developers were required to upload icon images as squares, but Apple's portal would promptly round off the corners.

Apple app developer portal - sharp icons for iOS 7

Image courtesy of AppleInsider, and supplied originally by AppNext

It's yet another hint that iOS 7 will be starkly different in appearance to previous versions. Noted minimalist Sir Jony Ive has been closely involved in the development of iOS 7, and it is believed he has been pushing for the app icons to be flatter, cleaner and more consistent. A supposedly leaked screenshot of iOS 7 earlier this week seemed to show simpler icons for Apple's own apps, with gloss, borders and texture effects removed. But they were still in Steve Jobs' favourite shape: the rounded square. This would be taking things to the next level.

Apple is expected to unveil new versions of its iOS mobile operating system - as well as an update to its OS X desktop and laptop platform - at its WWDC 2013 conference on Monday night. Stay tuned to Macworld UK for all the news and developments, as they happen.

[Related: iOS 7 release date, rumours and leaked images | What to expect from Apple at WWDC 2013 | Leaked iOS 7 screen suggests 'cleaner' app icon redesign | iOS 7 to be 'very, very flat']