The next iteration of iOS won't support the iPhone 3GS, according to an unconfirmed rumour.

MacStories reports that Mobile-Review.com editor-in-chief and MRG analyst Eldar Murtazin tweeted: "Apple iPhone 3Gs wont be upgradable to iOS 5.x. iPhone 4 will."

However, he didn't provide any more details or elaborate on where he had picked up the information, leaving it open to doubt.

iOS 5 and iPhone 5: What to expect

Apple is likely to put an end to the speculation one way or another at the WorldWide Developer Conference (WWDC) in early June, with beta versions of iOS 5 likely to be announced followed by the full version in the autumn, probably at the same time as the launch of the next-generation iPhone.

Last month, Apple reportedly began internal testing of iOS 5, which offered clues as to the company's plans to create its own satnav app. Other features thought to be coming to iOS 5 include a cloud-based 'music locker' and wireless syncing and updating.

iOS 4.3 was the first version of iOS not to support the iPhone 3G, though Apple did subsequently release iOS 4.2.8, containing a number of security updates for older handsets.