Apple's Tim Cook slams BBC report

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.

Tim Cook, CEO, Apple
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Tim Cook, CEO, Apple

Claims of poor working conditions at Apple suppliers have been made before with Chinese firm Foxconn—which also works with rival Sony—the center of scrutiny.

In October 2013, Foxconn admitted that student interns at one of its factories had worked shift patterns that are in violation of company policies. In October 2012, it admitted that it had employed interns as young as 14 years old, and there have also been reports of protests and violence at the company's manufacturing plants.

Meanwhile, Cupertino, California-based Apple is under investigation in Canada over claims that it used the popularity of its iPhones to unfairly negotiate with mobile carriers, according to Reuters. The news agency detailed allegations that Apple may have tried to encourage carriers to either maintain or increase the price of rival mobile phones. Apple was ordered by the Federal Court of Canada on Wednesday to turn over documents relating to the investigation.