A coronavirus variant first found in India is now officially a ‘variant of concern,’ the W.H.O. said.

Amid a deepening crisis in India, the World Health Organization announced Monday that it had designated the B.1.617 variant, which has been growing more common in the country, as a variant of concern. Scientists still don’t know much about the variant yet, but they are worried that it may be helping to fuel the rise in the nation’s coronavirus infections, which experts say are likely undercounted.

“There is increased transmissibility demonstrated by some preliminary studies” of the variant, said Dr. Maria Van Kerkhove, the technical lead of the W.H.O.’s coronavirus response.

Dr. Van Kerkhove also said that a study of a limited number of patients, which had not yet been peer reviewed, suggested that antibodies from vaccines or infections with other variants might not be quite as effective against B.1.617. However, the agency said that vaccines will likely remain potent enough to provide protection against B.1.617.

More details will be released in a report on Tuesday, Dr. Van Kerkhove said.

The variant was first detected in India at the end of 2020 but became more common in the country starting in March. It has since been found in 32 countries including the United States and the United Kingdom. The W.H.O.’s announcement comes as growing numbers of medical experts are adding their voices to a chorus of condemnation of the Indian government’s response and calling for nationwide restrictions to try to limit the horrifying death toll.

Although the official figures are already staggering — more than 350,000 new infections daily this month and nearly 250,000 total deaths — some experts say that the numbers are a vast undercount and estimate that India is on pace to suffer more than one million deaths by August.

Initially, the W.H.O. classified B.1.617 as a “variant of interest,” because it had certain mutations that have been linked to higher transmission and the potential to evade vaccines. At a news conference on Monday, agency officials announced they were elevated it to a higher level.

Other variants of concern include B.1.1.7, which was first identified in the United Kingdom, and P.1., which was originally detected in Brazil.

But experts caution that it’s not yet clear just how much of a factor B.1.617 has played in the catastrophic rise in cases in India. They point to a perfect storm of public health blunders, such as permitting massive political rallies and religious festivals in recent months.

“I am concerned about 617 — I think we have to keep a very close eye on it,” said Kristian Andersen, a virologist at Scripps Research Institute in La Jolla, California. But he cautioned that relatively few variant samples are being analyzed in India, making it hard to know just how dangerous B.1.617 is. “We really, really need better data out of India,” he said.

Over the weekend, the Indian Medical Association said in a statement it was time for a “complete, well-planned, pre-announced” lockdown to replace the scattershot regional restrictions currently in place across the nation of 1.4 billion.

The association said it was “astonished to see the extreme lethargy and inappropriate actions from the Ministry of Health in combating the agonizing crisis born out of the devastating second wave of the Covid-19 pandemic.”

Much of the criticism has been directed at Prime Minister Narendra Modi and his government, which allowed hundreds of thousands to gather at a large religious festival and held campaign rallies even as the virus surged.

An editorial published on Saturday in The Lancet, a medical journal, said that Mr. Modi “seemed more intent on removing criticism” on social media than “trying to control the pandemic.”

“India squandered its early successes in controlling Covid-19,” the editorial said.

The medical journal also cited an estimate by the Institute for Health Metrics and Evaluation that projected that India would witness a total of more than a million coronavirus deaths by August — far higher than government figures would suggest.

On May 2, for example, the institute said that total deaths were actually about 642,000, about three times higher than the government’s own number for that date, just over 217,000.

Referring to the possibility that there may actually be a million victims by August, the Lancet editorial said, “If that outcome were to happen, Modi’s government would be responsible for presiding over a self-inflicted national catastrophe.”

On Monday, India recorded more than 365,000 new cases and 3,754 deaths, according to data from the Health Ministry.

Dr. Ashish K. Jha, dean of the School of Public Health at Brown University, wrote in a tweet on Sunday that it was likely that between two to five million people were being infected every day and that India’s “true” coronavirus death toll was “closer to 25,000 deaths” each day.

He based his own calculations, he wrote, on the number of cremations taking place in the country.