UN High Commissioner for Human Rights Zeid Ra'ad al-Hussein told the BBC that attacks on the Rohingya had been "well thought out and planned" and he had asked Myanmar's leader Aung San Suu Kyi to do more to stop the military action.
Zeid has already called the campaign "a textbook example of ethnic cleansing" and asked rhetorically if anyone could rule out "elements of genocide", but his latest remarks put the case plainly, toughening his stance.
“The elements suggest you cannot rule out the possibility that acts of genocide have been committed,” he said.
“It’s very hard to establish because the thresholds are high,” he said. “But it wouldn’t surprise me in the future if the court were to make such a finding on the basis of what we see.”
Zeid said Myanmar's "flippant" response to the serious concerns of the international community made him fear the current crisis “could just be the opening phases of something much worse”.
Almost 870,000 Rohingya have fled to Bangladesh, including about 660,000 who arrived after Aug. 25, when the Myanmar army launched a crackdown.
UN investigators have heard Rohingya testimony of a "consistent, methodical pattern of killings, torture, rape and arson".
More villages burned
Meanwhile, Human Rights Watch said Monday Myanmar's army burned down dozens of Rohingya homes within days of signing a refugee repatriation deal with Bangladesh, showing the agreement was a mere "public relations stunt", AFP reported.
The rights group, citing analysis of satellite imagery, said buildings in 40 villages were destroyed in October and November, increasing the total to 354 villages that had been partially or completely razed since last August.
Dozens of buildings were burned the same week Myanmar and Bangladesh signed a memorandum of understanding on November 23 to begin returning refugees from Bangladesh within two months, HRW said in a report.
"The Burmese army's destruction of Rohingya villages within days of signing a refugee repatriation agreement with Bangladesh shows that commitments to safe returns were just a public relations stunt," said , HRW's Asia director, in the report, adding safety pledges for returnees could not be taken seriously.
Last week the group Doctors Without Borders released a survey which found that nearly 7,000 Rohingya had been killed in the Rakhine violence.