"They have been suffering, they are being tortured and killed, simply because they uphold their Muslim faith," Francis said in his weekly audience at the Vatican.

The rebuke comes as UN officials dealing with almost 70,000 Rohingya who have fled to Bangladesh refugee camps expressed concern the outside world has not fully grasped the severity of the crisis unfolding in Myanmar's western Rakhine State, home to almost one million Rohingya, who are denied basic rights, including citizenship in the country where they have lived for generations.

"The talk until now has been of hundreds of deaths. This is probably an underestimation – we could be looking at thousands," a UN official told Reuters.

The pope expressed concern about the plight of Rohingya in 2015 but his latest comments are his strongest yet on the issue, and will intensify pressure on Myanmar's military to end a brutal crackdown in Rakhine, following attacks on several border police posts last October.

Francis said the Rohingya have been "thrown out of Myanmar, moved from one place to another because no one wants them."

"But they are good people, peaceful people. They are not Christian….they are our brothers and sisters," he said.

The UN released a devastating report on February 3 detailing atrocities that it concluded raised serious concern that "ethnic cleansing" was underway to force Rohingya from Myanmar, the country also known as Burma.

It cited more than 200 witnesses and survivors to mass rapes, murders, forced disappearances, beatings and families locked in torched houses and burnt alive.

Among the atrocities was the slitting of a baby's throat as he cried out for his mother's milk while she was being gang raped. The report also detailed the case of a pregnant mother, whose stomach was stomped, while she was in labour.

For months Myanmar's government led by Nobel laureate Aung San Suu Kyi has denied multiple reports detailing the atrocities, including from Amnesty International, Human Rights Watch and Fortify Rights, and criticised the media for reporting them.

On Wednesday, Myanmar's Ministry of Foreign Affairs issued a  statement saying it was "deeply concerned" about the "very serious" allegations detailed in the UN report" and said the country would "spare no effort to take legal action against any perpetrators if there is clear evidence of human rights abuses."

But the ministry blamed the violence on "armed men funded and inspired from abroad," referring to reports that the attacks on the border posts were orchestrated by Muslim extremists based in Pakistan.

The government has referred the UN report to an already established investigation commission headed by a former general that rejected reports of abuses after its members visited Rakhine.

Adama Dieng, the UN's special adviser on the prevention of genocide, has called for an independent commission to investigate the abuses, saying the government-appointed commission is not credible or up to the task.

Ms Suu Kyi, who led her National League for Democracy to a landslide victory at elections in late 2015, has been widely criticised for failing to protect the Rohingya in the Buddhist majority country since violence erupted in Rakhine in 2012, displacing more than 100,000 from their homes.

For decades she stood up to despotic generals who ruled the country under brutal repression for half a century, winning admiration as democracy champion.

But observers in Myanmar believe she still has no control over the military which controls key security ministries.

Ultra-Buddhist nationalists regard Rohingya as illegal immigrants from Bangladesh who have no cultural or religious links to the Myanmar.

Meanwhile, foreign diplomats and non-government-organisations are alarmed at reports that Bangladesh plans to move tens of thousands of Rohingya from refugee camps at the border with Myanmar to low-lying islands off-shore.

"You don't put 100,000 people on an island where there is today nothing…without any preparation. It's terrible," a diplomat was quoted as saying in the Bangladesh capital Dhaka.