Apple has temporarily pulled down the iOS 9.3 update for older versions of iPad and iPhone following issues with device activation. Devices affected include iPhone 4s, 5c and 5s, third and fourth generation Retina iPads and the iPad Air.

According to posts on Apple's Support Communities site and tweets on the Apple Support Twitter page, some users are reporting that after installing the update, their devices are "bricked" or will not activate, leaving them unusable.

The issue, however, seems to affect the iPad 2 in particular where users are receiving an authentication error message, when they try to activate their iPads after installing the update.

Apple recently pushed out the iOS 9.3 build 13E236 for affected iPad 2 models and may be planning to release updates for additional devices in the next few days. The version released earlier this week was 13E234 on iPhone and 13E233 on iPad.

On Apple's support page, the company has said that while installing the update, users need to use their Apple ID and password, however, if they do not remember it, the activation could get stuck.

"Updating some iOS devices – iPhone 5s and earlier, and iPad Air and earlier – to iOS 9.3 can require entering the Apple ID and password used to set up the device in order to complete the software update. In some cases, if customers do not recall their password, their device will remain in an inactivated state until they can recover or reset their password. For these older devices, we have temporarily pulled back the update and will release an updated version of iOS 9.3 in the next few days that does not require this step," Apple said on its support page.

For users who have already installed iOS 9.3 and their devices are "bricked", Apple has published a support document with potential work arounds. The company recommends users try and reset their password, disable the Activation Lock feature via iCloud or try connecting the affected device to a computer running iTunes.

Released earlier this week, the latest version of Apple's mobile operating system includes a series of new features including Night Shift, Touch ID for Notes, new Apple Music options for CarPlay, additional Quick Actions for 3D Touch, a more personalised News app and more.

When Apple released iOS 9 in 2015, numerous iPhone users reported not being able to move beyond the "slide to upgrade" screen, WiFi connectivity issues and that Gamer Center was not working, among other issues. In 2014, the company's iOS 8 update forced the company to roll out a series of bug fixes for months.