Optus executives insist they weren't obliged to urgently notify officials multiple deaths were linked to a major triple-zero outage, defending a near-18-hour delay in providing key details.

Staff at the embattled telco learned before 9pm on September 18 multiple fatalities had been tied to the catastrophic outage, but they waited until the following afternoon to let the industry regulator and minister know.

Under-fire executives from Optus copped a parliamentary bashing on Monday for their response to the triple-zero failure and three linked deaths.

More than 600 triple-zero calls could not be connected, but the telco initially suggested to authorities the number involved was just a handful.

Optus chief executive Stephen Rue said the company wanted to complete welfare checks on those a

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