Veteran US diplomat Bill Richardson has resigned from an international panel set up by Myanmar leader Aung San Suu Kyi to advise on the Rohingya crisis.
He claimed the panel was a "whitewash" and accused Ms Suu Kyi, his long-time friend, of lacking "moral leadership".
Myanmar said he should "review himself" over the "personal attack".
More than 650,000 Rohingya people, from a mostly-Muslim minority in Buddhist Myanmar, fled to Bangladesh last year in the face of a military crackdown.
Many are now living in refugee camps in the neighbouring country. Bangladesh has said they will all be returned to Myanmar within two years.
Mr Richardson added that Ms Suu Kyi had been "furious" when he raised the case of two Reuters reporters on trial in Myanmar.
Mr Richardson, a former adviser to the Clinton administration, has known Ms Suu Kyi for decades, and visited the Nobel laureate while she was under house arrest in the 1990s.
He told Reuters he was resigning from the advisory board because it was a "whitewash" and he did not want to be part of a "cheerleading squad for the government".
He was "alarmed by the lack of sincerity with which the critical issue of citizenship was discussed," he wrote in a statement.
The military offensive that led to a mass exodus from Myanmar's northern Rakhine state has been described by the United Nations as a "textbook example of ethnic cleansing" – something Myanmar denies.
There were around one million Rohingya people in Myanmar at the start of 2017, where they have their own language and culture. But the government sees them as illegal immigrants from Bangladesh and denies them citizenship.
In August last year, after Rohingya militants attacked police posts, people started to flee across the border. Arriving in Bangladesh, they told repeated stories of troops, backed by local Buddhist mobs, burning villages and attacking and killing civilians.
Mr Richardson said he had got into an argument with Ms Suu Kyi during a meeting on Monday after he raised the case of two Reuters reporters who are on trial for breaching the Official Secrets Act. The journalists were working on coverage of the Rohingya crisis at the time.
Ms Suu Kyi "exploded" at him when he mentioned the journalists, he told the New York Times.
"Her face was quivering, and if she had been a little closer to me, she might have hit me, she was so furious," Mr Richardson said.
Mr Richardson went on to say he had been "taken aback by the vigour" with which she had "disparaged" the media, the UN, human rights groups and the international community during three days of meetings.
And, on Ms Suu Kyi herself, he said: "She's not getting good advice from her team.
"I like her enormously and respect her. But she has not shown moral leadership on the Rakhine issue and the allegations made, and I regret that."
A Myanmar government spokesman said Mr Richardson "should review himself over his personal attack against our State Counsellor".
Mr Richardson had raised the case of the reporters at an unrelated meeting about Rakhine, Zaw Htay said. "We feel sorry for his resignation due to the misunderstanding."
The Advisory Board for the Committee for Implementation of the Recommendations on Rakhine State was set up by Ms Suu Kyi's government last year.
Until Mr Richardson resigned, the board had 10 members, five of whom are from overseas.
One of those, former South African Defence Minister Roelof Meyer, travelled with the board's remaining members to Rakhine state on Wednesday.
He told Reuters the visit had been "very constructive", and said any suggestion the board was "just a rubber stamp or a voice on behalf of the government… would be completely untrue, unfair. We haven't done any recommendations so far."