The Wall Street Journal has reported that Apple has been testing iPhones with screen sizes of between 4.8-inches and 6-inches.
A 6-inch iPhone would be two inches bigger than the current iPhone 5 model and could be classed as a phablet: a tablet that functions as a phone with screen sizes of 5 to 7 inches.
Rival smartphone company Samsung already offers phablets in the form of the 5.7-inch Galaxy Note 3 and the 6.3-inch Galaxy Mega.
Apple currently offers an iPad mini at 7.9-inches, but it does not have phone capabilities. The iPhone 5S and cheaper iPhone 5C are currently in development, but are expected to be the same size as the current iPhone 5 model.
The iPhone 5S is expected to feature a fingerprint sensor, which could be used for unlocking the home screen or confirming identity for online payments.
New high-resolution images published on Thursday by Sonny Dickson show a circular component that is presumed to fit underneath the iPhone home button, with a fingerprint scanning mechanism at its centre.
A recent report by market research firm IDC revealed that phablets overtook shipments of both laptops and tablets in Asia in the second quarter of 2013. The growth of phablets was primarily due to adoption in emerging markets, according to IDC.
