Widespread atrocities against Rohingya Muslim women and girls have been orchestrated and perpetrated by Myanmar's military and may amount to war crimes, crimes against humanity and genocide, the UN envoy on sexual violence in conflict said on Wednesday.

Pramila Patten, who met many Rohingya victims of sexual violence in Bangladesh camps during a visit this month, said she fully endorses the assessment by UN human rights chief Zeid Ra'ad Al Hussein that Rohingya have been victims of “ethnic cleansing.”

Patten said at a news conference that the widespread use of sexual violence “was clearly a driver and push factor” for more than 620,000 Rohingya to flee Myanmar.

It was “also a calculated tool of terror aimed at the extermination and removal of the Rohingya as a group,” she added.

Myanmar's government has denied committing any atrocities as has its military.

The government refused a request from Patten to visit northern Rakhine state where many Rohingya lived.

Buddhist-majority Myanmar doesn't recognise the Rohingya as an ethnic group, insisting they are Bengali migrants from Bangladesh living illegally in the country.

It has denied them citizenship, leaving them stateless.

The recent spasm of violence began when Rohingya insurgents launched a series of attacks August 25.

Myanmar security forces then began a scorched-earth campaign against Rohingya villages that the UN and human rights groups have called a campaign of ethnic cleansing.

Patten said that during her visit to camps for the displaced, she heard “the most heartbreaking, most shocking, and horrific accounts of abuses committed cold-bloodedly with unparalleled hatred against the Rohingya community.”

Patten, a former member of the UN Committee on the Elimination of all Forms of Discrimination Against Women, said sexual violence including gang rape by soldiers, forced public nudity and sexual slavery and it was clearly being used “as a tool of dehumanisation and as a form of punishment.”

She said a number of eyewitnesses “reported rapes of the most extreme and brutal nature, which included the tying of women and girls to a rock or tree before being gang raped by multiple soldiers and many were literally gang-raped to death.”

Some girls who were raped in their houses were left to die when their houses were torched, she added.

Witnesses also said that even before August 25, Myanmar troops would throw Rohingya babies into fires or into village wells to contaminate the water and deprive residents of drinking water, Patten said.

“My observations point to a pattern of widespread atrocities, including sexual violence against Rohingya women and girls who have been systematically targeted on account of their religion and ethnicity,” said Patten, a lawyer from Mauritius.

“And a clear picture has emerged about the alleged perpetrators of these atrocities and their modus operandi,” she said.

“The sexual violence has been commanded, orchestrated, and condoned and perpetrated by the armed forces of Myanmar, the Tatmadaw.

And other actors involved include the Myanamar border guard police and militia composed of Rakhine Buddhists and other ethnic groups.”

Patten said the UN population agency has provided services to 1,644 survivors of various forms of sexual and gender-based violence.

“My guess is that this is the tip of the iceberg,” she said.

Patten said she believes “there is a prima facie case for pursuing these atrocities in an international court, especially given that the sexual violence was targeted against the women on the basis of their religion and ethnicity as a form of collective punishment and persecution against the group as a whole.”

“I can also see a basis for characterising these violations as war crimes, crimes against humanity and acts of genocide, but it is not my role to make that determination,” she said.

Patten said she plans to participate in a Human Rights Council meeting on Myanmar in Geneva on December 5 and hopes to be able to brief the Security Council in New York on sexual violence against Rohingya on December 12.

The council would have to refer Myanmar to the International Criminal Court for the violence against Rohingya to be considered as possible war crimes.

That appears highly unlikely as China, an ally of Myanmar, is one of the council's five powers that can veto any action.

Nonetheless, Patten said she plans to meet with the court's prosecutor, Fatou Bensouda, next month at U.N. headquarters in.