(CNN) Puerto Rico's governor defended his government's efforts to account for deaths on the island following Hurricane Maria after a new study called the official tally a "substantial underestimate."

The official death toll in Puerto Rico has been the subject of substantial controversy since Hurricane Maria hit the island, a US territory, on September 20. Gov. Ricardo Rosselló said he welcomed the results of a Harvard study published Tuesday in the New England Journal of Medicine.

Researchers surveyed 3,299 randomly chosen households across the island and compared it to official mortality statistics from 2016. They concluded that an estimated 4,645 people died in Hurricane Maria and its aftermath in Puerto Rico -- almost 70 times the government's official tally of 64.

Rosselló said he does not stand by the official death toll. But he said his government did the best it could with information-gathering protocol available to them at the time.

"We had established that this number was going to be much, much higher than what we had as an official tally," he told CNN's Anderson Cooper. "It's not sticking with the number. It was just establishing that the process that we had prior led us to that number, which is what we got from doctors and death certificates."

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