Further delays could mar the upcoming release dates of the iPhone 5S, its low-cost version and the rumoured iPhone 6, analysts said.

The iPhone refresh, according to Glen Yeung of Citigroup Capital Markets, could come as late as September this year or two months earlier from KGI Securities' prediction last week that the iOS smartphone would only start selling on November.

Mr Yeung revealed in a new note to investors that Apple has encountered "volume production issues," that would inevitably pushback the launch date earlier set for both the iPhone 5S and its more affordable edition.

In another report coming from news agency Reuters, it was indicated that Apple remains enmeshed in the issue of finding the best coating for its planned fingerprint sensor that will be embedded on the iPhone's Home button.

The problem alone will surely pushback the tech giant's production calendar, thereby affecting its flagship release dates that were originally set for June or July this year, the same report said.

In the same note reported by CNET, Mr Yeung also shared his sentiments regarding the rumoured budget iPhone and phablet coming from Apple.

"We do not expect iPhone 6 and remain unclear on low-end iPhone," the analysts said, referring to the high probability that the large-screen Apple smartphone will have to wait for its launch date until next year.

Another thing that could delay Apple's anticipated iPhone refresh this year is the report that Tim Cook, Apple CEO, could be on his way out following increased pressure from the company board over the rapidly decreasing share prices of the tech titan.

If the reports proved true, Apple could be issuing its banner products this year without the man who immediately succeeded the late Steve Jobs.