Sources in Japan and Taiwan tell the site that they initially expected mass production to begin in June; however, that date may now have slipped further away.
The phone, widely referred to as the iPhone 5S, is expected to include new features such as a fingerprint sensor. A supply chain source in Taiwan said Apple was trying to find a coating material that did not interfere with the fingerprint sensor, and this may be causing a delay.
It's also said that Apple is developing a cheaper model of the iPhone which could appeal to low income buyers in emerging markets.
A supplier source in Japan told Reuters small-scale production of display panels will begin in May, ramping up to mass production in June. Both phones will use the same 4-inch screen, but the cheaper version will probably not include the new fingerprint technology and sport a cheaper plastic casing, the sources said.
This aligns with a recent report from KGI Securities analyst Ming-Chi Kuo who adjusted previous estimates to suggest the iPhone 5S would ship at earliest in September.