CANBERRA - The Australian government said on Tuesday that it is investigating five social media platforms for failing to comply with the country's world-first social media ban for children younger than 16.

In its first report on the social media minimum age obligation, the federal government's eSafety Commissioner said on Tuesday that it has "significant concerns" about the compliance of the social media giants, including Facebook and Instagram, with the laws that came into effect in December.

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Under those laws, social media companies that fail to take reasonable steps to prevent children younger than 16 from accessing their platforms face fines worth up to 49.5 million Australian dollars ($33.9 million).

The eSafety Commissioner report said that it has identified "poor practices," including platforms allowing children to repeatedly attempt age assurance methods to obtain a 16+ outcome and failing to provide pathways for reporting age-restricted accounts.

It said that the five platforms have been notified about the specific issues and an investigation into potential non-compliance has commenced.

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Australia's Minister for Communications Anika Wells said in a statement that she expects the online safety watchdog to "throw the book" at companies that have systematically failed to uphold their legal obligations.

"If these companies want to do business in Australia, they must obey Australian laws," she said.

The eSafety Commissioner, Julie Inman Grant, said that her office is now moving into an enforcement stage of the social media ban.