Apple chief executive Tim Cook has responded to media reports alleging harsh working conditions in China for manufacturing employees of the popular gadget-maker.

Cook, who took over as chief executive from Apple's late co-founder, Steve Jobs, addressed the reports of long hours and occasionally unsafe conditions in an email obtained by the 9to5mac.com website.

Cook's message comes after The New York Times and other media outlets published stories about working conditions in factories in China which make parts or assemble Apple devices such as the iPhone and the iPad.

"As a company and as individuals, we are defined by our values," Cook said in the email. "Unfortunately some people are questioning Apple's values today, and I'd like to address this with you directly."

The Times report cited safety issues and said workers assembling iPhones, iPads and other devices "often labor in harsh conditions" and work "excessive overtime."

The newspaper said two explosions at iPad factories last year killed four people and injured 77.

"We care about every worker in our worldwide supply chain," Cook said. "Any accident is deeply troubling, and any issue with working conditions is cause for concern.

"Any suggestion that we don't care is patently false and offensive to us," he said. "As you know better than anyone, accusations like these are contrary to our values. It's not who we are.

"For the many hundreds of you who are based at our suppliers' manufacturing sites around the world, or spend long stretches working there away from your families, I know you are as outraged by this as I am," Cook said.

Apple was inspecting more factories and this month opened up its supply chain for independent evaluations by the Fair Labor Association, he said.

"Every year we inspect more factories, raising the bar for our partners and going deeper into the supply chain," Cook said. "We've made a great deal of progress and improved conditions for hundreds of thousands of workers.

"We know of no one in our industry doing as much as we are, in as many places, touching as many people," he said.

"We are attacking problems aggressively with the help of the worlds foremost authorities on safety, the environment, and fair labor," he said.

"We will continue to dig deeper, and we will undoubtedly find more issues," Cook said. "What we will not do -- and never have done -- is stand still or turn a blind eye to problems in our supply chain. On this you have my word."

Apple did not immediately respond to a request for comment.