Escalating violence has forced more than 650,000 Rohingya Muslims to flee across the border to Bangladesh, in what the UN's human rights chief has described as a "a textbook example of ethnic cleansing".
Special Rapporteur Yanghee Lee said the atrocities against the Rohingya Muslim minority "bear the hallmarks of genocide".
"The body of information and materials we are collecting is concrete and overwhelming", the experts of the Fact-Finding Mission said in their oral report.
Adama Dieng spent a week in Bangladesh to assess the condition of the nearly 700,000 Rohingyas who had fled across the border from Myanmar, and he said during his trip he heard "terrifying stories".
In response to a question last month about the most prominent of Myanmar's hardline nationalist monks, Wirathu, whose one-year preaching ban has recently expired, Facebook said it suspends and removes anyone who "consistently shares content promoting hate".
The group detailed "gross human rights violations", including indiscriminate shooting at fleeing villagers, burning of elderly and children alive in their homes, hacking people to death, and sexual violence towards women and girls.
The United Nations Special Adviser on the Prevention of Genocide, Adama Dieng, has strongly criticized the worldwide community for ignoring atrocities committed by Myanmar authorities, accusing them of burying their "head in the sand".
Another U.N. investigator said on Monday that Myanmar had launched new military operations against the Rohingya. "As far as the Myanmar situation is concerned, social media is Facebook, and Facebook is social media".
UN Myanmar investigator Yanghee Lee credited Facebook with helping the predominately Buddhist country of Myanmar to communicate.
Lee said the platform had "turned into a beast".
"Any denial of the seriousness of the situation in Rakhine, the reported human rights violations, and the suffering of the victims, is untenable", they said. "We are ready to take action, where there is the evidence", he said.
Independent journalists have been barred from visiting the area, aside from rare government-escorted tours, and Myanmar has arrested two Reuters reporters for their detailed coverage documenting the killings.
Since then there have been multiple reports of state-led violence against the refugees, and the United Nations has been leading a fact-finding mission in the country.
Myanmar's military had also advanced into Mutraw District in Kayin State, an area controlled by the Karen National Union, despite a ceasefire agreement, she said.
Myanmar government spokesman Zaw Htay in an undated photo.
"Of course, there is always more we can do and we will continue to work with local experts to help keep our community safe".
"Whether or not we consider that the crimes committed amount to crimes against humanity or genocide, this should not delay our resolve to act and to act immediately". Adama Dieng, who this past week visited Bangladesh's refugee camps and met officials, also urged the UN Security Council to hold Myanmar to account over the "international crimes".
Bangladesh and Myanmar agreed in November to begin repatriating Rohingya who volunteered to return to Rakhine, but the plan has stalled. Translated by Khet Mar.