Apple usually launches the newest version of its iPhone in September.
The company did not immediately return emails seeking comment.
Analysts and media reports have said Apple may launch two iPhone models with 4.7 and 5.5 inch screens this year to compete with Samsung Electronics Co Ltd's popular Galaxy Note 3 phablets, which have a 5.7 inch display.
Apple's current iPhone models, the 5S and 5C, have a 4 inch display panel.
The company has asked suppliers to manufacture 70-80 million units of the new large-screen iPhones by the end of the year, the Wall Street Journal reported in July.
Apple's shares were down 0.8 per cent at $94.81 in late afternoon trading on Tuesday.