Local telecommunications operator Singtel has apologised for a service outage involving its Australian subsidiary Optus that resulted in the deaths of three people.In an SGX filing on Wednesday (Sept 24), Singtel group CEO Yuen Kuan Moon said that the company is «deeply sorry» for the outage on Sept 18 and that it is working with Optus to «ensure a thorough investigation of this incident to prevent any future recurrence».«Optus has been co-operating fully and transparently with all relevant government agencies and regulatory bodies while the matter is being investigated and will share the findings in due course,» said Yuen.The outage was caused by a departure from regular processes during a network upgrade, which sparked a technical failure and subsequently disrupted emergency call services for 13 hours.Some 600 customers across South Australia, Western Australia and the Northern Territory were affected by the glitch, and three deaths have been linked to it. The death of an 8-week-old boy was initially linked to the disruption, but the claim was later dismissed by police, ABC News reported.  Read more