Six photos were posted by Twitter user @mornray886 today with the caption "iPhone 6 #Apple"
Australian writer Sonny Dickson tells MacRumors that the images were initially shared by someone in China who claimed the images show the "iPhone 6." Twitter is anonymous, so the photos should be taken with a large grain of salt.
MacRumors notes that the images lack plastic or glass cutouts for antennas, and that the images show FCC text on the rear bezel which is typically added much later in the development cycle. The iPhone 6 has been rumored to land in September and FCC text wouldn't usually show up on prototypes seven months before release.
The other possibility is that Apple could be planning to release the iPhone 6 sooner than its typical fall launch timeframe, possibly as a response to Samsung's Galaxy S5 which is expected to be announced at Mobile World Congres on February 24, 2014 – a month earlier than the Galaxy S4 arrived last year.