Apple has previously refused to comment on speculation that it may be working on iPhones with larger screens.
Apple has previously been rumoured to be working on larger screen phones.
Back in the middle of summer, a number of reports emerged suggesting that the company was investigating the alternative screen sizes. At the time, it was put down to pressure to respond to the growth of Android.
The WSJ report also reiterates previous rumours suggesting that the iPhone 5S will come with a fingerprint scanner. Apple is holding an event on Tuesday where it is widely expected to officially unveil its next generation of iPhones.
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Commentators have noted that companies often test different sizes of products and that nothing may come of these trials. They add that even if Apple does decide to launch smartphones with larger screens, it is unlikely to do so for another year.