Burma security forces killed hundreds of men, women and children during a systematic campaign to expel Rohingya Muslims, Amnesty International has said in a new report.
More than 580,000 refugees have arrived in Bangladesh since August 25, when Burma security forces began a scorched-earth campaign against Rohingya villages.
Burma's government has said it was responding to attacks by Muslim insurgents, but the United Nations and others have said the response was disproportionate.
The continuing exodus of Rohingya Muslims has become a major humanitarian crisis and sparked international condemnation of Buddhist-majority Burma, which still denies atrocities are taking place.
Based on interviews with more than 120 fleeing Rohingya, Amnesty International said at least hundreds of people were killed by security forces who surrounded villages, shot fleeing inhabitants and then set buildings alight, burning to death the elderly, sick and disabled who were unable to flee.
In some villages, women and girls were raped or subjected to other sexual violence, according to the report.
The witnesses repeatedly described an insignia on their attackers' uniforms that matched one worn by troops from Burma's Western Command, Amnesty International said.
When shown various insignia used by Burma's army, witnesses consistently picked out the Western Command patch, it said.
The 33rd Light Infantry Division and border police, who wear a distinctive blue camouflage uniform, were also frequently involved in attacks on villages, along with Buddhist vigilante mobs, witnesses said.
Matthew Wells, an Amnesty crisis researcher who spent several weeks at the Bangladesh-Burma border, said the rights group plans to issue another report in the coming months examining individual criminal responsibility, including specific commanders and others that may be involved in abuses.
He said hundreds of Rohingya have been treated for gunshot wounds and doctors say that the injuries are consistent with people being shot from behind as they fled.
There were credible indications that a total of several hundred people had been killed in just five villages that were the focus of Amnesty's reporting. Mr Wells said that given that dozens of villages across northern Rakhine State have been targeted in a similar fashion, the death toll could be much higher.
He said satellite imagery, corroborated by witness accounts, show that Rohingya homes and mosques have been burned entirely in villages, while non-Rohingya areas just one or two hundred yards away were untouched.
"It speaks to how organised, how seemingly well-planned this scorched-earth campaign has been by the Myanmar military and how determined the effort has been to drive the Rohingya population out of the country," Mr Wells said.
Among almost two dozen recommendations, the human rights group called for the UN Security Council to impose a comprehensive arms embargo on Burma and financial sanctions against senior officials responsible for violations that Amnesty says meet the criteria for crimes against humanity.
It said the council should explore options for bringing the perpetrators to justice under international law if Burma authorities do not act swiftly.
"It is time for the international community to move beyond public outcry and take action to end the campaign of violence that has driven more than half the Rohingya population out of Myanmar," Amnesty International said.