Apple Inc yesterday announced it would \"thoroughly investigate\" an accident in which a woman in northwest China was suspected of being killed by an electric shock when making a phone call with a recharging iPhone 5. Ma Ailun, a 23-year-old flight attendant with China Southern Airlines, was picking up her iPhone 5 to answer a call while the battery was being charged when she was electrocuted and killed last Thursday, police said Sunday. But police have not confirmed whether a mobile phone was involved as they continue to investigate the case. A spokeswoman for the technology company said: \"We are deeply saddened to learn of this tragic incident and offer our condolences to the ... family. We will fully investigate and co-operate with authorities in this matter.\" Ma, who was planning her wedding on August 8, fell to the floor when making a call with her iPhone 5, which was being recharged at the time, Ma\'s sister said on her microblog account. Ma Ailun bought the iPhone in December at an official Apple store and was using the original charger to recharge the phone when the incident occurred, her sister said. \"I want to warn everyone else not to make phone calls when your mobile phone is recharging,\" she tweeted. The sister\'s tweet was reposted more than 3,000 times. And the microblogging site was flooded with posts urging fellow users not to make calls while charging their phones. Experts said mobile phones have a low output of only 3 to 5 volts, which isn\'t enough to harm the human body. People will feel an electric shock at about 36 volts. \"However, if the charger or the circuit has a problem, such as a broken wire, it can lead to a shock of 220 volts,\" a senior physics teacher at a Nanjing high school was quoted as saying in a media report. Xu Xuelu, an expert with the Nanjing Appliance Repairing Association, recommended people avoid making calls with their mobile phone while it is being recharged. In 2010, a man in northeast China was killed by an electric shock when making a phone call with a handset that was being recharged with an unauthorized charger, according to the China Consumers Association.