Jeff Williams, Apple's senior vice president for operations, has responded to a BBC report that workers at Asian suppliers for the iPhone 6 are mistreated and overworked, saying he's "deeply offended" by the accusations.

In an email to some 5,000 Apple staff in the United Kingdom, Williams hit back at the British broadcaster's Panorama program, which sent in undercover reporters to observe conditions at the Pegatron factory, near Shanghai, where iPhones are assembled.

The BBC's report "implied that Apple isn't improving working conditions," said Williams in the email published by The Telegraph, the authenticity of which NPR confirmed with Apple.

"Let me tell you, nothing could be further from the truth," he wrote.

"We know of no other company doing as much as Apple does to ensure fair and safe working conditions, to discover and investigate problems, to fix and follow through when issues arise, and to provide transparency into the operations of our suppliers," Williams wrote to employees.

But, he added, "We can still do better. And we will."

Panorama has stood by its reporting that rules on workers' hours, ID cards, dormitories and work meetings were routinely breached, according to the BBC. the documentary alleged that workers fell asleep during 12-hour shifts on the iPhone production line and that some of them were required to work 18 days at a stretch.

Williams responded that Apple had tracked the weekly hours of more than 1 million workers in its supply chain and that 93 percent were in compliance with a limit of 60 hours per week.

Panorama also reported that child labor was being used in Indonesia tin mines, where some of the raw materials for iPhones are procured.

In response, Williams said in the email: "Apple has publicly stated that tin from Indonesia ends up in our products, and some of that tin likely comes from illegal mines.

"Tens of thousands of artisanal miners are selling tin through many middlemen to the smelters who supply to component suppliers who sell to the world," Williams wrote. "[There] is widespread corruption in the undeveloped supply chain. Our team visited the same parts of Indonesia visited by the BBC, and of course we are appalled by what's going on there."

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