Tim Cook, the CEO of Apple, has struck out at U.K. broadcaster BBC over allegations of poor working conditions at its suppliers working on the iPhone 6.

Apple's senior vice-president of operations, Jeff Williams, sent an email to around 5,000 staff members in the U.K. on Friday, saying that he and Cook were "deeply offended" by the BBC's claims.

The letter follows an undercover investigation by the broadcaster, screened Thursday evening, which made allegations that employees at the Pegatron factories, near Shanghai, were treated poorly. It also accused Apple of "routinely" breaking promises to protect workers.

"(The BBC's) report implied that Apple isn't improving working conditions," said Williams in the letter, which was first reported by the U.K.'s Telegraph newspaper. "Let me tell you, nothing could be further from the truth."

The BBC footage claimed to show exhausted workers falling asleep on 12-hour shifts and one undercover reporter having to work 18 days in a row despite "repeated" requests to take a day off. The same documentary reported from Indonesia, showing children digging tin ore by hand in what it called "extremely dangerous conditions." The program claimed that the tin was being sold to a company that is on Apple's list of suppliers.



Apple declined to comment when contacted by CNBC Friday but told the BBC that it strongly disagreed with the documentary's conclusions.



"We are aware of no other company doing as much as Apple to ensure fair and safe working conditions," it told the British news broadcaster. "We work with suppliers to address shortfalls, and we see continuous and significant improvement, but we know our work is never done."

Apple added that it was investigating the evidence but said it was "very common practice" for workers to nap during break times. It also said that it was dedicated to the ethical sourcing of minerals.



Read the full report on the BBC website.