An Indian state has raised its Covid-19 death toll sharply higher after the discovery of thousands of unreported cases, lending weight to suspicion that India's overall death tally is significantly more than the official figure.

But the discovery of several thousand unreported deaths in the state of Bihar has raised suspicion that many more coronavirus victims have not been included in official figures.

The health department in Bihar, one of India's poorest states, revised its total Covid-19 related death toll to more than 9,429 from about 5,424.

The newly reported deaths had occurred last month and state officials were investigating the lapse, a district health official said, blaming the oversight on private hospitals.

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