Apple has sent independent medical experts to a Shanghai factory operated by supplier Pegatron after the deaths of some employees.
"While they have found no evidence of any link to working conditions there, we realise that is of little comfort to the families who have lost their loved ones," Apple said. "We have a team working with Pegatron at their facility to ensure that conditions meet our high standards."
Apple has for years faced questions about working conditions at plants of suppliers that provide components and assemble its top-selling iPhones and iPads. It has published audits disclosing instances of child labour, long working hours, unfair compensation and practices that cause harm to the environment.
Several workers at Pegatron (Shanghai) "passed away in a short period of time", China Labor Watch (CLW) said in a Monday statement without saying how many workers, whether they worked on Apple products, or how the labour group obtained the information. Pegatron also supplies Sony and Dell.
A 15-year-old died of pneumonia on October 9 at a Shanghai hospital after taking a pre-employment physical examination on September 4 which indicated he was in good health, CLW wrote without saying whether the test included a lung examination or checked for signs of pneumonia.
Apple's suppliers code of conduct requires workers to be aged at least 15. "Pegatron has strict measures in place to verify workers' ages before and after they are hired, and we work with health and safety experts to provide a safe working environment for each and every worker," the Taipei-based company said. "We have an excellent track record of compliance with laws aimed at preventing under age labour."
Apple chief executive officer Tim Cook has made improving conditions within its supply chain a priority and says the company will suspend business with those that violate its code of conduct. The company last year enlisted the Fair Labor Association to perform independent reviews of its suppliers.
Pegatron, spun off as the manufacturing arm of Asustek Computer in 2010, is the second company after Foxconn Technology to assemble iPhone and iPads, according to Apple's supplier report. Quanta Computer makes computers for Apple.
CLW said Pegatron made tablet computers and mobile phones.