A United Nations report on Monday called for Myanmar's military leaders, including the commander in chief, to be investigated and prosecuted for genocide, crimes against humanity and war crimes over their actions in ethnic and religious minority states — the strongest international condemnation yet of the military's actions following a crackdown on Rohingya Muslims last August.

The report, the culmination of interviews, research and analysis by a U.N.-mandated fact-finding mission conducted for more than a year, significantly challenges the Myanmar military's decades-long assertions, both in Rakhine state and elsewhere, that it is merely responding to security challenges. The fact-finding mission went beyond the military's actions in Rakhine and investigated the military's conduct more broadly since 2011, a time when the world was cautiously celebrating the country's opening to the West and nominally democratic transformation.

It found "patterns of gross human rights violations and abuses committed in Kachin, Rakhine and Shan state" that "undoubtedly amount to the gravest crimes under international law," a statement announcing the report's findings said.

"Military necessity would never justify killing indiscriminately, gang raping women, assaulting children and burning entire villages," said the report. The armed forces' "tactics are consistently and grossly disproportionate to actual security threats."

The fact-finding mission concluded that there is "sufficient information" to open a genocide and war crimes investigation of senior Myanmar generals. A spokesman for Myanmar's armed forces could not be reached for comment.

On Monday, just after the U.N. report was released, Facebook took a rare step, removing 18 Facebook accounts, one Instagram account and 52 Facebook pages — including that of the commander in chief, Min Aung Hlaing. The accounts were followed by 12 million people.

"International experts, most recently in a report by the U.N. Human Rights Council-authorized fact-finding mission on Myanmar, have found evidence that many of these individuals and organizations committed or enabled serious human rights abuses in the country," Facebook said. "We want to prevent them from using our service to further inflame ethnic and religious tensions."

The U.N. report extends culpability for the humanitarian crisis in Rakhine state to Myanmar's civilian government, led by Nobel laureate Aung San Suu Kyi. The civilian government, the report said, has failed to speak out against unfolding events, spread "false narratives," oversaw the destruction of evidence and blocked independent investigations.

"Through their acts and omissions, the civilian authorities have contributed to the commission of atrocity crimes," it said.

The report will "have a big impact internationally, coming from the main U.N.-mandated body investigating the violence against the Rohingya, and also covering armed conflict in Shan and Kachin states," said Richard Horsey, a former U.N. diplomat in Myanmar. "Its specific finding that there is sufficient grounds for investigation and prosecution of military commanders for genocide is likely to have particularly serious diplomatic, not only legal, consequences."

However, Myanmar's government has rejected the mandate of the fact-finding mission from its inception.