An analyst claimed that tech giant Apple's upcoming smartphones will most likely be delayed due to "preproduction issues".

According to Jefferies analyst Peter Misek, the rumoured low cost iPhone 5S will most likely be delayed. Misek also said that the possible cheaper iPhone launch could be pushed to this year's fourth quarter and an iPhone 6 probably would not come out until 2014.

"iPhone 5S is having preproduction issues with mass production at least a month or more away. This combined with the publicly discussed delay of iOS 7 puts a July availability at risk. We continue to believe there is almost no chance the iPhone 6 launches in CY13 [calendar year 2013] due to supply chain issues," Misek said.

Another analyst predicted a possible delay on iPhones' release date this year. According to a report by KGI Securities analysts Ming-Chi Kuo, people should expect to see the aforementioned device later this year.

Kuo said that part of the problem with the iPhone 5S products lies in the rumored fingerprint sensor that Apple is adding. Finding the right color coatings to prevent interference with the sensor has been an unforeseen challenge.

Along with the delays on the physical production of the iPhone 5S, rumours also say that Apple's been hard pressed to get iOS 7 finished in time. Thanks to the significant changes pushed by Jony Ive, Apple has pulled engineers off of OS X 10.9 to help get iOS 7 finished by this summer. Last year, the iOS 6 beta was revealed months before the iPhone 5, so keep in mind that Apple doesn't necessarily need to finish the iPhone 5S by the time iOS 7 is ready.

The rumour is fuelled by the speculation that the release iPhone 6 and iPhone 5S will be postponed due to US carrier T-Mobile's delayed availability of the current iPhone. It has been less than a week since T-Mobile announced the long-awaited release of the iPhone 5 on its network free of contract. The smartphone will make its debut with T-Mobile on April 12. Pre-orders for the handset began for the iPhone 5 on Friday.

With the delayed availability of the handset in T-Mobile, Apple may not release the successors of the handset yet. Rumours claimed that Apple is set to unleash iPhone 6 and iPhone 5S in June.

Some of the rumoured features of the next iPhone are Retina or IGZO screen display, A7 quad core chip processor, iOS 7, 128GB internal storage, 13 mega-pixel camera, and longer battery life. The lack of NFC support on the iPhone 5 was one of the biggest criticisms aimed at Apple's smartphone.

The low cost iPhone 5S, on the other hand, is rumoured to sport a plastic casing, 4-inch screen display, dual core processor and 8-megapixel camera.

As usual, Apple did not comment on the rumours about iPhone 6 or iPhone 5S.