Optus is pledging to fully investigate a 10-hour triple-zero outage, accepting responsibility for a number of breakdowns during which at least four people died.

The telco's chief executive says an independent investigation will be conducted after admitting the outage was caused by a botched firewall update to the system.

Stephen Rue admitted Optus had been contacted by the telecommunications industry ombudsman about two complaints of people trying to inform the company about the outage.

"Early review suggests that we had not handled these calls as would be expected," he told reporters in Sydney on Saturday.

"Optus will be appointing an independent person to lead a review into this entire incident from every aspect, I hope to confirm that person in coming days."

Optus was unaware of Th

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