Jyoti Sanghera, head of the Asia and Pacific region of the UN human rights office, called on Myanmar leader Aung San Suu Kyi to "stop the violence" and voiced fear that if the stateless Rohingya refugees return from Bangladesh they may be interned.
"If villages have been completely destroyed and livelihood possibilities have been destroyed, what we fear is that they may be incarcerated or detained in camps," she told a news briefing.
In a report based on 65 interviews with Rohingyas who have arrived in Bangladesh in the past month, it said that "clearance operations" had begun before insurgent attacks on police posts on Aug 25 and included killings, torture and rape of children.
"Credible information indicates that the Myanmar security forces purposely destroyed the property of the Rohingyas, scorched their dwellings and entire villages in northern Rakhine State, not only to drive the population out in droves but also to prevent the fleeing Rohingya victims from returning to their homes," the report said.
It said the destruction by security forces, often joined by mobs of armed Rakhine Buddhists, of houses, fields, food stocks, crops, and livestock made the possibility of Rohingyas returning to normal lives in northern Rakhine "almost impossible".
"We are not in a position to make a finding of genocide or not, but this should in no way detract from the seriousness of the situation which the Rohingya population is currently facing," said Thomas Hunecke, who led the team that went to Cox's Bazar, Bangladesh, between Sept 14 and 24.
It was "highly likely" that Myanmar security forces planted landmines along the border in recent weeks to prevent Rohingyas from returning, he said, citing doctors treating injuries.
Violence continues
Despite growing international condemnation of the crisis, the military campaign is popular in Buddhist-majority Myanmar, where there is little sympathy for the Rohingyas, and for Muslims in general, and where Buddhist nationalism has surged.
Myanmar on Tuesday launched its first bid to improve relations between Buddhists and Muslims since the eruption of deadly violence inflamed the communal tension and triggered an exodus of some 520,000 Muslims to Bangladesh.
The UN experts documented Myanmar security forces "firing indiscriminately at Rohingya villagers, injuring and killing other innocent victims, setting houses on fire".
"Almost all testimonies indicated that people were shot at close range and in the back while they tried to flee in panic," the report said.
"It was a situation of panic – they shot my sister in front of me, she was only seven years old. She cried and told me to run. I tried to protect her and care for her, but we had no medical assistance on the hillside and she was bleeding so much that after one day she died. I buried her myself."
The girl did not know what happened to her mother and four brothers, nor her father jailed a month earlier.