The United Nations boss has called for action to end "violence" against the Rohingya, pleading with the Myanmar government to immediately end military operations against the majority-Muslim ethnic group.

In a speech to the UN Security Council on Thursday, Antonio Guterres said the current crisis is "steadily deteriorating", adding that since the conflict began last month about 500,000 Rohingya have already crossed the border to Bangladesh to flee the violence in Myanmar's Rakhine State.

"The situation has spiralled into the world's fastest developing refugee emergency - a humanitarian and human rights nightmare," Guterres said.

"The reality on the ground demands action. Swift action, to protect people, alleviate suffering, prevent further instability, address the root causes of the situation and forge a long lasting and durable solution."

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He urged Myanmar's government to allow humanitarian access to the conflict region, as well as allow "voluntary return" of refugees to their areas of origin.

The Rohingya, a marginalised and stateless people in Buddhist-majority Myanmar, have been fleeing to Bangladesh amid reports of atrocities committed by the army.



Earlier this week, a UN agency said that up to 700,000 Rohingya refugees had fled their homes to other parts of Myanmar or Bangladesh.

Guterres said that of the hundreds of thousands of people displaced, more than 90 percent are Rohingya.

"We have received bone-chilling accounts from those who fled, mainly women, children and the elderly," he said. "These testimonies point to excessive violence and serious violations of human rights."

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Guterres also cautioned that the current conflict risks the possibility of "radicalisation" among the refugees, as well as trafficking of women and children.

The International Organization for Migration (IOM) also said it has been receiving increasing reports that Rohingya have been sexually assaulted in Rakhine state.

In response to Guterres' comments, Thaung Tun, Myanmar's national security adviser, told the UN Security Council that there is no ethnic cleansing against Rohingya.

He blamed the violence that forced the Rohingya to flee to Bangladesh on the Arakan Rohingya Solidarity Army (ARSA) armed group.

"The vast majority of those who fled did so out of fear - fear was instilled in the hearts by the terrorists," he said referring to ARSA.

Earlier on Thursday, scores of Rohingya refugees were feared drowned after trying to flee to Bangladesh from Myanmar.