A worker at Apple's iPhone manufacturing plant in Zhengzhou, visited by CEO Tim Cook just a few months ago, has been found dead, reigniting concerns over how the iGiant's Chinese outsourcer Foxconn treats its employees.

Foxconn, dubbed Mordor by Apple engineers, said in a statement that it was cooperating with the authorities over the circumstances of the 28-year-old male employee's death. He was found outside a building on its campus in central China earlier this week.

While Foxconn did not state the cause, New York-based non-profit China Labor Watch has said it was suicide – the worker jumped to his death from a building – reflecting a number of other similar incidents in the past few years.

The factory in question was visited by Apple CEO Tim Cook in October last year where he posed for pictures and praised the "talented people" there who have helped build the latest iPhone model, the iPhone 6.

In 2010, no fewer than six Foxconn employees killed themselves and two others attempted suicide, reportedly over working conditions. One leapt to his death after allegedly being roughed up by Foxconn security in their search for a misplaced Apple iPhone 4G prototype.

In January 2012, a group of workers at a Foxconn factory in Wuhan threatened to jump off the roof of the factory after bosses went back on an offer to provide one month's wages as severance pay. That factory made parts for Microsoft's Xbox gaming console.

In December 2013, Apple sent medical experts to a Chinese factory run by another manufacturer – Pegatron, which builds the company's iPhones – after a teenaged boy died from pneumonia. That death again raised concerns over the sweatshop-style working conditions (Apple's team concluded the conditions were not to blame).

And in spring 2013, three workers from the same factory as the most recent death committed suicide in just three weeks, according to China Labor Watch. Those deaths were reportedly in response to a new workplace policy of not allowing any talking on the job or risk being faced with immediate dismissal.

Foxconn is one of the world's largest contract manufacturers and has a workforce of over one million people in China. In response to the deaths and poor conditions, the company raised its wages in 2010, and opened itself up to audits of its conditions in 2012. It also says it has introduced suicide-prevention programs at its factories.

With a workforce that size – the equivalent of a big Western city – suicides are bound to happen, statistically speaking.

But this isn't a city, it's a multibillion-dollar company, and employees aren't statistics. Concerns exist over conditions, including safety, overtime, and a lack of unions to look out for the workers' best interests. ®