The State Department study, based on interviews in April with 1,024 Rohingya adults who have taken refuge in neighboring Bangladesh, provided accounts consistent with reports from human rights groups but kept largely to dispassionate descriptions of events.
The report notably did not use the terms genocide or ethnic cleansing to describe the mass killings of the Rohingya, a mostly Muslim group concentrated in Rakhine state that is despised by many in Buddhist-majority Myanmar and who are not considered citizens.
"The survey reveals that the recent violence in the northern Rakhine state was extreme, large-scale, widespread and seems geared toward both terrorizing the population and driving out the Rohingya residents," said the report by the State Department's Bureau of Intelligence and Research.
"The scope and scale of the military's operations indicate they were well-planned and coordinated," it said.
"In some areas, perpetrators used tactics that resulted in mass casualties, for example, locking people in houses to burn them, fencing off entire villages before shooting into the crowd or sinking boats full of hundreds of fleeing Rohingya."
The report said 82 percent of the interviewed refugees personally witnessed killings, with 51 percent also reporting sexual violence.
"They would then choose a smaller number of women -- often four or five, but some refugees reported up to 20 -- whom as many as 15 soldiers would then take to fields, forests, houses, schools, mosques or latrines to gang rape," it said.
"Many victims were reportedly killed afterward, though not in all cases," it said, adding that soldiers in some cases would go door to door to find the "prettiest girls" to gang-rape.
In an overwhelming 88 percent of cases, the witnesses said the military was behind the atrocities. Few said they saw attacks against them by the Arakan Rohingya Salvation Army (ARSA), the Islamic militant group whose assaults on military posts in October 2016 triggered the crackdown.
The violence in Myanmar, formerly known as Burma, was unleashed soon after the country transitioned to democracy, undermining what Western governments had hailed as a triumph of engagement.
The campaign against the Rohingya has especially tarnished the reputation of Aung San Suu Kyi, the long-detained democracy advocate and Nobel laureate who has been reticent in addressing the violence.
Meanwhile, Britain hosted a meeting of about a dozen foreign ministers that was also attended by Myanmar's state counselor Kyaw Tint Swe and International Cooperation Minister Kyaw Tin, although Suu Kyi did not come to New York.
"If in a year's time, we have not made a meaningful difference to the lives of the million or more people affected, then we have failed as an international community," Hunt told the closed meeting, according to the spokesperson.
Myanmar's army chief Min Aung Hlaing was recently quoted in a newspaper as telling his troops that no country, organization or group has the "right to interfere in and make the decision over sovereignty of a country".