Key Apple assembler Hon Hai Precision Industry, also known as Foxconn Technology Group, has been studying the possibility of moving iPhone production to the U.S., sources told the Nikkei Asian Review.

"Apple asked both Foxconn and Pegatron, the two iPhone assemblers, in June to look into making iPhones in the U.S.," a source said. "Foxconn complied, while Pegatron declined to formulate such a plan due to cost concerns."

Foxconn, based in the gritty, industrial Tucheng district in suburban Taipei, and its smaller Taiwanese rival churn out more than 200 million iPhones annually from their massive Chinese campuses.

Another source said that while Foxconn had been working on the request from Apple Inc., its biggest customer that accounts for more than 50% of its sales, Chairman Terry Gou had been less enthusiastic due to an inevitable rise in production costs.