A U.S. research group has said that India’s coronavirus death toll is up to 10 times higher than the nearly 415,000 fatalities reported by authorities.

The Center for Global Development study’s estimate is the highest yet for the carnage in the South Asian nation of 1.3 billion people, which is emerging from a devastating surge partly fueled by the Delta variant in April and May. The study — which analyzed data from the start of the pandemic to June this year — suggested that between 3.4 million and 4.7 million people had died from the virus.

“True deaths are likely to be in the several million, not hundreds of thousands, making this arguably India’s worst human tragedy since partition and independence,” the researchers said.

India’s official death toll of just over 414,000 is the world’s third-highest after the United States’ 609,000 fatalities and Brazil’s 542,000.

Experts have been casting doubt on India’s toll for months, blaming the stressed health service rather than deliberate misinformation.

Meanwhile, several Indian states have revised their virus tolls in recent weeks, adding thousands of “backlog” deaths.