The military crackdown in Myanmar's Rakhine state could be leading to genocide, the United Nations' top official on the subject says.

More than 140,000 Rohingya Muslims have fled to Bangladesh since August 25, bringing allegations of mass killings and the systematic burning of their villages by Myanmar security forces.

The violence was sparked when Rohingya insurgents carried out coordinated attacks against police posts, killing 12 officers.

Retaliation from soldiers, the paramilitary Border Guard Police and Buddhist vigilantes has killed at least 370 people, according to the army's figure from almost a week ago.

But there are credible reports of 130 people massacred in a single village, including women and children.

"When they are being killed and forcibly transferred in a widespread or systematic manner, this could constitute ethnic cleansing and could amount to crimes against humanity," Adama Dieng, the UN special advisor for the prevention of genocide, said.

"In fact it can be the precursor to all the egregious crimes — and I mean genocide.

"We are not yet there, we cannot say we are facing a genocide, but it is time to take action."

Sorry, this video has expired Reports of villagers slaughtered in Myanmar massacre

The difference between ethnic cleansing and genocide

While the terms "crime against humanity" and "genocide" are legally defined under an international convention, ethnic cleansing is not.

Genocide was defined in 1948 — after the Jewish Holocaust — as being an intentional action to destroy an ethnic, national, racial, or religious group, in whole or in part.

"I would hesitate to say at the moment that there is a genocide [in Myanmar], although that's mainly for lack of evidence — it's still a plausible conclusion," David Simon, director of the genocide studies program at Yale University, said.

"I think we can say with a fair amount of certainty that there is ethnic cleansing going on and certainly crimes against humanity."

Responsibility to protect

In the wake of the genocide in Rwanda — during which UN peacekeepers were withdrawn at the height of the slaughter — the UN developed a doctrine known as responsibility to protect, or R2P.

The idea was that sovereign states have a duty to protect people living within its borders, including visitors and the stateless.

A code of conduct sets out three levels of involvement: the country taking responsibility for protecting its population, the international community assisting the country with that protection, and failing that, intervention — including the use of force through the UN Security Council.

"If this idea of 'responsibility to protect' is meant to be a universal doctrine, this would clearly seem to be a place where it applies," Mr Simon said.

The UN Security Council met to discuss Myanmar last week and there are calls for stronger action.

"I have written officially to the president of the Security Council to express my concern and to propose various steps to end the violence and address the underlying causes of the crisis," UN Secretary-General Antonio Guterres said.

"The international community must undertake concerted efforts to prevent any further escalation and to seek a holistic solution."

Myanmar has defended the violence as a justified response to a threat from "extremist Bengali terrorists" — the term the Government requested local media to use for the Arakan Rohingya Salvation Army.

De-facto leader of the country Aung San Suu Kyi has been criticised for not speaking up for Rohingyas, but she has no control over the army.

The Rohingya people have faced a long history of persecution. ( AP Photo/Bernat Armangue) )

Unwilling to intervene

Persecution and sporadic outbreaks of violence are not new for the Rohingya people.

In a recent report, the Burma Human Rights Network catalogued abuses dating back to 1938, when 240 Muslims were killed.

A flare up in 2012 sent Rohingyas fleeing and left 120,000 stranded in camps, totally dependent on humanitarian aid to survive.

That is in addition to the approximately 400,000 Rohingyas who live in refugee camps across the border in Bangladesh, where they are also not formally recognised.

Despite the long history of persecution and the intensity of the recent violence, the director of Yale University's Genocide Studies Centre said it was unlikely the UN would send in peacekeepers.

"Sovereignty remains the ultimate trump card," Mr Simon said.

He said the decision of when to step in is made on the basis of sheer suffering.

"The international community is extremely unwilling to violate sovereignty, I think absent the types of numbers that we saw in Rwanda," Mr Simon said.

"So as long as the reports come out of refugee camps on the Bangladesh side of the border that hundreds or thousands of people are being killed, it's not enough to move the needle all the way towards intervention, which is a cold reality of how these things are determined."