An ambitious effort by the World Health Organization to calculate the global death toll from the coronavirus pandemic has found that vastly more people died than previously believed — a total of about 15 million by the end of 2021, more than double the official total of 6 million reported by countries individually.

But the release of the staggering estimate — the result of more than a year of research and analysis by experts around the world and the most comprehensive look at the lethality of the pandemic to date — has been delayed for months because of objections from India, which disputes the calculation of how many of its citizens died and has tried to keep it from becoming public.

More than one-third of the additional 9 million deaths are estimated to have occurred in India, where the government of Prime Minister Narendra Modi has stood by its own count of about 520,000. The WHO will show the country’s toll is at least 4 million, according to people familiar with the numbers who were not authorized to disclose them, which would give India the highest tally in the world, they said. The New York Times was unable to learn the estimates for other countries.