Facebook has long been accused of helping spread vast amounts of hate speech against the Rohingya before hundreds of thousands of them were driven into neighbouring Bangladesh in a crackdown now subject to a UN genocide investigation.

In late 2021, Rohingya refugees sued Facebook for $150 billion, claiming the social network failed to stem the hate speech directed against them.

Now, the United Nations' Independent Investigative Mechanism for Myanmar (IIMM) says there is clear evidence that Myanmar's military secretly orchestrated the hate speech campaign.

The military had in a "systematic and coordinated" manner "spread material designed to instil fear and hatred of the Rohingya minority", the investigators said in a fresh report.

"It accomplished this by creating a clandestine network of pages on a social media site with the potential to reach an audience of millions."

The IIMM was established by the UN Human Rights Council in 2018 to collect evidence of the most serious international crimes and prepare files for criminal prosecution.

Its new analysis looked at content posted on 43 Facebook pages between July and December 2017.

That report found the seemingly unrelated pages, most of them with no outward affiliation to the military and including some devoted to celebrity news and popular culture, "were part of a network with clear ties to the Myanmar military".

The report identified 10,485 items with hate speech on the pages, and which Facebook removed from its platform in August 2018.

The "hate speech content often played upon prevalent discriminatory and derogatory narratives concerning the Rohinguya, ranging from the narrative that the Rohingya pose an existential threat to Myanmar through violence, terrorism or 'Islamisation'," it said.

Some of the hate speech also played "to the narrative that they pose a threat to Burmese racial purity through their alleged rampant breeding".

The connections between the pages were seen in various ways, including that they often shared creators, administrators, and editors, and regularly posted material using the same IP addresses used by the Myanmar military.

"Identical material was often posted on multiple pages in this network, sometimes within minutes," the IIMM said.