Investigators working for the UN's top human rights body said Monday that Myanmar military leaders should be prosecuted for genocide against Rohingya Muslims, taking the unusual step of identifying six by name among those behind deadly, systematic crimes against the ethnic minority.

The call, accompanying a first report by the investigators, amounts to some of the strongest language yet from UN officials who have denounced alleged human rights violations in Myanmar since a bloody crackdown began last August.

The three-member "fact-finding mission" working under a mandate from the UN-backed Human Rights Council meticulously assembled hundreds of accounts by expatriate Rohingya, satellite footage and other information to assemble the report.

A Rohingya refugee boy desperate for aid cries as he climbs on a truck distributing aid for a local NGO near the Balukali refugee camp last September in Cox's Bazar, Bangladesh. UN investigators say the situation in Myanmar should be referred to the International Criminal Court. (Kevin Frayer/Getty Images)

"The military's contempt for human life, dignity and freedom — for international law in general — should be a cause of concern for the entire population of Myanmar, and to the international community as a whole," said fact-finding mission chair Marzuki Darusman, a former Indonesian attorney-general, at a news conference.

The council created the mission in March last year — nearly six months before a string of deadly rebel attacks on security and police posts set off a crackdown that drove Rohingya to flee into neighbouring Bangladesh. The UN estimates that more than 700,000 have fled.

Facebook used to incite violence

Investigators also sharply criticized Facebook, which despite its limited direct presence in Myanmar (also known as Burma) has become the country's dominant social media network despite having no employees there, for letting its platform be used to incite violence and hatred.

Facebook responded on Monday by announcing it was blocking 20 Myanmar officials and organizations found by the UN panel to have "committed or enabled serious human rights abuses."

The company already acknowledged this month that it had been "too slow" to respond to incitement in Myanmar.

'Conservative' estimate of 10,000 killed

The team compiled accounts of crimes including gang rape, the torching of hundreds of villages, enslavement, and killings of children — some before the eyes of their own parents. The team was not granted access to Myanmar and has decried a lack of co-operation or even response from the government, which received an early copy of the report.

The team cited a "conservative" estimate that some 10,000 people were killed in the violence, but outside investigators have had no access to the affected regions — making a precise accounting elusive, if not impossible.

Above all, the investigators said the situation in Myanmar should be referred to the International Criminal Court, and if not, to a special tribunal. Last week, Myanmar's government rejected any co-operation with the ICC, to which it is not a party.

China, a permanent member of the UN Security Council with veto power over whether the issue will be brought before the ICC, has been reticent about condemning Myanmar's government during the crisis.

Shikira Arifullah, a 22-year-old Rohingya refugee woman from Guddumpara village, is helped from a boat as she arrives exhausted on the Bangladesh side of the Naf River at Shah Porir Dwip after fleeing her village in Myanmar, last October. (Kevin Frayer/Getty Images)

UN leaders, foreign government officials, and human rights watchers have for months cited evidence of genocide in Myanmar, and the United States late last year said that "ethnic cleansing" was occurring in Myanmar. But few experts have studied the issue as in-depth, and in such an official way, as the fact-finding mission with a mandate from the 46-nation council.

Determining 'genocidal intent'

The United Nations does not apply the word "genocide" lightly. The fact-finding team's assessment suggests the crimes against the Rohingya could meet the strict legal definition — which was last met over crimes in Bosnia and Rwanda nearly a quarter-century ago.

Human rights watchers say determining "genocidal intent" is perhaps the most difficult criterion to meet: In essence, it's the task of assessing the mindsets of perpetrators to determine if ethnicity, race, religion or another attribute had motivated them.

A Rohingya refugee camp is seen in Cox's Bazar, Bangladesh, on Sept. 19, 2017. The violent crackdown in Rakhine state led hundreds of thousands of Rohingya to flee to neighbouring Bangladesh. (Cathal McNaughton/Reuters)

"The crimes in Rakhine state, and the manner in which they were perpetrated, are similar in nature, gravity and scope to those that have allowed genocidal intent to be established in other contexts," the report said, alluding to a region of Myanmar that is home for many Rohingya.

Adding into their assessment:

The extreme brutality of the crimes.

"Hate rhetoric" and specific speech by perpetrators and military commanders.

Policies of exclusion against Rohingya people.

An "oppressive context."

The "level of organization indicating a plan for destruction."

The investigators cited six Myanmar military leaders by name as "priority subjects" for possible prosecution, led by the commander-in-chief, Min Aung Hlaing.

A longer list of names is to be kept in the office of the UN human rights chief for possible use in future judicial proceedings. The United States and European Union have already slapped sanctions on some Myanmar military leaders, though Min Aung Hlaing is not among them.

"The main perpetrator, the people that we want the spotlight on, is the Tatmadaw," said mission member Radhika Coomaraswamy, a Sri Lankan former UN undersecretary-general, referring to Myanmar's military.

Call for resignation

The fact-finding panel said Min Aung Hlaing should step down following its call for his prosecution.

"The only way forward is to call for his resignation and stepping down immediately," Marzuki Darusman, chairman of the Independent International Fact-Finding Mission on Myanmar, said at a Geneva news conference.

Listen to Radhika Coomaraswamy, a member of the Independent International Fact-finding Mission on Myanmar, describe the sexual violence inflicted on Rohingya:

One member of UN fact-finding group, Radhika Coomaraswamy, spoke about sexual violence against Rohingya Muslims in Myanmar 0:48

Contacted by phone ahead of the news conference, Maj.-Gen. Tun Tun Nyi, Myanmar military spokesperson, said he could not immediately comment on the UN report.

Bob Rae, Canada's special envoy to the Rohingya crisis, says the international community faces tough legal challenges if it hopes to prosecute military leaders for genocide.

In his report released earlier this year, Rae said the prosecution of crimes against humanity needed to be pursued and urged Canada to play a leading role.

While he stopped short of using the genocide label — as have many Western governments — Rae said Monday's finding puts more pressure on the international community to find a forum to prosecute those named by UN investigators.

He said that would not be an easy task.

Christopher Sidoti, an Australian human rights expert, acknowledged that no "smoking gun" linked the six military leaders directly to orders to carry out genocide, but pointed to inferences of their role based on a strict chain of command in Myanmar.

The authors called for the creation of a special body, or "mechanism," to keep watch on the still-evolving human rights situation in Myanmar.

Criticism of Myanmar's Nobel-winning leader

They said the United Nations' own role in the country since 2011 should be reviewed to see if the world body did all it could to prevent such a crisis.

The authors also faulted Aung San Suu Kyi for not using her role as head of Myanmar's government, nor her "moral authority" — she is a Nobel peace prize laureate — to stop the events in embattled Rakhine state.

UN Secretary-General Antonio Guterres is scheduled to give a briefing Tuesday during a Security Council commemoration of the anniversary of the violent crackdown on the Rohingya. Guterres also has described what happened in Myanmar as ethnic cleansing.

UN spokesperson Stephane Dujarric told reporters Monday that Guterres urged all UN bodies and the international community to seriously consider the experts' report recommendations. The determination of whether "a genocide" occurred must be made by "an international judicial body," Dujarric said.

"The secretary-general has for a long time underscored the violations of human rights in Myanmar" and stressed "that accountability is essential for genuine reconciliation," he said.

Forum-Asia, an advocacy group, called the report "significant" and said the United Nations needed to heed its call.

"If the UN fails to adequately address these findings it will be a monumental failure for the world body, which has already been criticized for not doing enough," said R. Iniyan Ilango, UN advocacy program manager for the group.

Praise also came from the ground in Cox's Bazar, Bangladesh, where refugee camps have taken in hundreds of thousands of Rohingya from across the border.

"We are happy for this. If these army people are punished the world will take note of it. They are killers. They must be punished," said Mohammed Hasan, 46, who lives in the Kutupalong refugee camp.

"They killed thousands; we have seen that. They torched our homes. That's a fact. They raped our women. That's not false," he said.

With files from The Canadian Press and Reuters