SAN JUAN, Puerto Rico — Puerto Rico’s governor raised the U.S. territory’s official death toll from Hurricane Maria from 64 to 2,975 on Tuesday after an independent study found that the number of people who succumbed in the desperate, sweltering aftermath had been severely undercounted.

The new estimate of nearly 3,000 dead in the six months after Maria devastated the island in September 2017 and knocked out the entire electrical grid was made by researchers with the Milken Institute School of Public Health at George Washington University.

“We never anticipated a scenario of zero communication, zero energy, zero highway access,” Gov. Ricardo Rossello told reporters. “I think the lesson is to anticipate the worst. … Yes, I made mistakes. Yes, in hindsight, things could’ve been handled differently.”

He said he is creating a commission to study the hurricane response, and a registry of people vulnerable to the next hurricane, such as the elderly, the bedridden and kidney dialysis patients.

Rossello acknowledged Puerto Rico remains vulnerable to another major storm. He said the government has improved its communication systems and established a network to distribute food and medicine, but he noted that there are still 60,000 homes without a proper roof and that the power grid is still unstable.

“A lesson from this is that efforts for assistance and recovery need to focus as much as possible on lower-income areas, on people who are older, who are more vulnerable,” said Lynn Goldman, dean of the Milken institute.

Tuesday’s finding is almost twice the government’s previous estimate, included in a recent report to Congress, that there were 1,427 more deaths than normal in the three months after the storm.

The George Washington researchers said the official count from the Sept. 20 hurricane was low in part because doctors were not trained in how to classify deaths after a disaster.

The number of deaths from September 2017 to February 2018 was 22 percent higher than during the same period in previous years, Goldman said.

The number of dead has political implications for the Trump administration, which was accused of responding half-heartedly to the disaster. Shortly after the storm, when the official death toll stood at 16, President Donald Trump marveled over the small loss of life compared to that of “a real catastrophe like Katrina.”

Hurricane Katrina, which struck New Orleans in 2005, was directly responsible for about 1,200 deaths, according to the National Hurricane Center. That does not include indirect deaths of the sort the George Washington researchers counted in Puerto Rico.

Rep. Nydia Velazquez, a New York Democrat, said the report shows the U.S. government failed the people of Puerto Rico.

“These numbers are only the latest to underscore that the federal response to the hurricanes was disastrously inadequate and, as a result, thousands of our fellow American citizens lost their lives,” she said in a statement.

There is no national standard for how to count disaster-related deaths. While the National Hurricane Center reports only direct deaths, such as those caused by flying debris or drowning, some local governments may include indirect deaths from such things as heart attacks and house fires.

Researchers with George Washington said they counted deaths over the span of six months — a much longer period than usual — because so many people were without power during that time.

“That caused a number of issues,” Goldman said, explaining that people were forced to exert themselves physically or were exposed to intense heat without fans or air conditioning. “It’s fairly striking that you have so many households without electricity for so long. That’s unusual in the U.S. after a disaster.”