FILE PHOTO: View of an Optus shop in Sydney, Australia November 8, 2023. REUTERS/Kirsty Needham/File Photo

By Renju Jose and Roshan Thomas

SYDNEY (Reuters) -Singapore Telecommunications, which owns Australia's second largest telco Optus, apologised on Wednesday for a Optus outage that probably caused four deaths, after emergency calls were disrupted in two states and the Northern Territory.

Singtel Group CEO Yuen Kuan Moon said the company was working with the Optus board to investigate last week's outage and prevent similar incidents in the future.

Optus has been cooperating with government agencies and regulatory bodies, he added.

"We are deeply sorry to learn about the network incident at our Optus subsidiary that has impacted triple-0 calls, and to hear that customers could not connect to emergency services when they most needed them," Yuen said in a statement.

Optus last week said an issue with a network firewall upgrade triggered a 13-hour outage that disrupted emergency call services and potentially affected around 600 customers, some in remote areas who were unable to make phone calls.

Anger over the outage has been growing in Australia, with Prime Minister Anthony Albanese calling it "completely unacceptable".

CEO Stephen Rue said on Wednesday that initial checks suggested the incident could have been caused by human error and admitted procedures were not followed during the outage.

Kerry Schott, non-executive director at AGL Energy, will lead an independent review into the technical failure, he added.

"While our internal investigations are ongoing, this independent review will identify the causes and canvass the applicable processes, protocols and operations of this instance," Rue said during a media briefing.

"The review will also examine the management of triple-0 calls in the Optus network, including the monitoring and operational effectiveness in relation to the technical failure."

The independent review is expected to be completed by year-end, with findings to be reported to the Optus board before being made public.

(Reporting by Roshan Thomas in Bengaluru and Renju Jose in Sydney; Editing by Alan Barona and Kate Mayberry)