Myanmar's security forces have committed mass killings and gang rapes of Rohingya Muslims and burned their villages since October in a campaign that probably amounts to crimes against humanity and possibly "ethnic cleansing", the UN human rights office said on Friday.
Witnesses had testified to "the killing of babies, toddlers, children, women and elderly; opening fire at people fleeing; burning of entire villages; massive detention; massive and systematic rape and sexual violence; deliberate destruction of food and sources of food", the report said.
One woman told UN investigators how her eight-month baby boy had had his throat slit. Another was raped by soldiers and saw her five-year-old daughter killed as she tried to stop them.
"The devastating cruelty to which these Rohingya children have been subjected is unbearable," UN High Commissioner for Human Rights Zeid Ra'ad al Hussein said in a statement.
Around 66,000 people have fled from the Muslim-majority northern part of Rakhine State to Bangladesh since Myanmar's military launched a security operation in response to attacks on police border posts on Oct 9, the UN report said. The UN humanitarian office has recently put the figure at 69,000.
"The 'area clearance operations' have likely resulted in hundreds of deaths," some of them through helicopters shooting at villages and dropping grenades on them, the UN report said.
Four UN investigators gathered testimony last month from 220 Rohingya victims and witnesses who fled the "lockdown area" in Maungdaw in Rakhine for the Cox's Bazar district in Bangladesh.
Nearly half reported a family member had been killed or disappeared while 101 women reported having been raped or subjected to sexual violence, it said.
The investigators took evidence including photographs of bullet and knife wounds, burns, and injuries resulting from beatings with rifle butts or bamboo sticks.
The plight of the stateless Rohingya, of whom some 1.1 million live in apartheid-like conditions in Rakhine, has long been a source of friction between Myanmar and Bangladesh.
Myanmar, a mostly Buddhist country where Nobel laureate Aung San Suu Kyi is de facto leader, has denied almost all allegations of human rights abuses in northern Rakhine and says a lawful counterinsurgency campaign is under way.
In Yangon, the spokesman for President Htin Kyaw's office, said the government had not yet seen the report.
"We will review the report from the UN and we will respond, either in an official statement or in an individual response (to questions)," Zaw Htay said.
While denying observers and independent journalists access to the conflict area, officials have accused Rohingya residents and refugees of fabricating stories of killings, beatings, mass rape and arson in collaboration with insurgents who they say are Rohingya terrorists with links to Islamists overseas.
Zeid called for a robust reaction from the international community and said Myanmar must accept responsibility for committing grave human rights violations against its own people.
The report said the attacks on the Rohingya "seem to have been widespread as well as systematic, indicating the very likely commission of crimes against humanity".
Bangladesh is determined to relocate Rohingya Muslims fleeing violence in Myanmar to an island in the Bay of Bengal, a Bangladeshi minister said on Wednesday. Critics say the island is uninhabitable. The minister said the move was temporary and Myanmar would ultimately have to take the Rohingya back.