Current supply shortages of the quick-selling iPhone 5 may be blamed on its complicated construction, one Taiwan-based manufacturer told the Wall Street Journal.

An unnamed official from the Hon Hai Precision Industry Company, which also uses the trade name Foxconn Technology Group, called Apple's newest smartphone, "the most difficult device that Foxconn has ever assembled.  To make it light and thin, the design is very complicated.”

The same official also told the WSJ that productivity is improving with practice, and new quality checks are in place to prevent the devices from shipping with scratches on the metal portion of the case.

Hon Hai workers assemble the iPhone 5 at its plants in Zhengzhou and Guan Lan, China.

Recent labor disputes at the company's Zhengzhou plant have also raised concerns about the manufacturer being able to keep up with demand.

“The Zhengzhou site, which was set up in 2011, is still pretty new to us. We are still learning how to manage the work force there,” the official told the WSJ, adding that hiring at the plant has been increased to meet Apple production demand.