UN Secretary-General Antonio Guterres has urged Burma's authorities to immediately end military operations that have sent over 500,000 Rohingya Muslims fleeing to Bangladesh, calling the crisis “the world's fastest developing refugee emergency and a humanitarian and human rights nightmare.”

The UN chief warned that the humanitarian crisis is a breeding ground for radicalisation, criminals and traffickers. And he said the broader crisis “has generated multiple implications for neighbouring states and the larger region, including the risk of inter-communal strife.”

Mr Guterres told the UN Security Council at its first open meeting on Burma since 2009 that government authorities must also allow “unfettered access” for humanitarian aid and ensure “the safe, voluntary, dignified and sustainable return” of all those who sought refuge across the border.

The Rohingya have faced decades of discrimination and persecution by the majority Buddhist population in Myanmar, where they are denied citizenship despite centuries-old roots in the country.

The current crisis erupted in August when an insurgent Rohingya group attacked police posts in Burma's Rakhine state, killing a dozen security personnel — an act that Mr Guterres again condemned.

The attacks prompted Burma's military to launch “clearance operations” against the rebels, setting off a wave of violence that has left hundreds dead, thousands of homes burned and the mass flight of Rohingya to Bangladesh.

Mr Guterres previously called the Rohingya crisis “ethnic cleansing.” He didn't use those words on Thursday but he referred to “a deeply disturbing pattern to the violence and ensuing large movements of an ethnic group from their homes.”

Rohingya refugees – in pictures Show all 15 1 /15 Rohingya refugees – in pictures Rohingya refugees – in pictures A young girl and a baby wade through mud after arriving in Whaikhyang, Bangladesh from Burma on 10 September Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya refugees walk through a camp in Whaikhyang, Bangladesh after arriving from Burma Dan Kitwood/Getty Images Rohingya refugees – in pictures A young Rohingya refugee gathers firewood after arriving in Whaikhyang, Bangladesh from Burma Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya refugees wait for sacks of rice to be distributed in Whaikhyang, Bangladesh Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya Muslim refugees arrive on a boat in Whaikhyang, Bangladesh after crossing from Burma on 8 September Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya Muslim refugees react after being re-united with each other after arriving in Whaikhyang, Bangladesh on a boat from Burma Getty Rohingya refugees – in pictures Rohingya Muslim refugees walk along the remains of a road after arriving in Whaikhyang, Bangladesh on a boat from Burma Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya Muslim refugees wade through water after arriving in Whaikhyang, Bangladesh by boat from Burma Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya Muslim refugees wade through water after arriving in Whaikhyang, Bangladesh by boat from Myanmar Dan Kitwood/Getty Images Rohingya refugees – in pictures Rohingya Muslim refugees stand in the rain after arriving in Whaikhyang, Bangladesh by boat from Burma Dan Kitwood/Getty Images Rohingya refugees – in pictures Indian children hold placards and shout slogans during a protest against the alleged persecution of the Rohingya Muslims in Burma EPA/Raminder Pal Singh Rohingya refugees – in pictures Supporters of the Difa-e-Pakistan Council (DPC), an Islamic organisation, listen to their leaders' speeches against Burma's persecution of Rohingya Muslims, during a demonstration in Karachi Reuters/Akhtar Soomro Rohingya refugees – in pictures Hundreds of Iranians take part in a protest against violence in Myanmar after weekly Friday prayers, in Tehran EPA/Abedin Taherkenareh Rohingya refugees – in pictures Indonesian Muslim activists hold placards and shout slogans during a protest against the alleged persecution of the Rohingya minority in Magelang, Central Java, Indonesia EPA/Ali Lutfi Rohingya refugees – in pictures Members of an Islamic organisation shout slogans against the Burma government during a protest in Dhaka, Bangladesh EPA

Burma authorities insist security operations ended in early September, but Mr Guterres said that “displacement appeared to have continued, with reports of the burning of Muslim villages, as well as looting and acts of intimidation.”

The UN chief cited Rathedaung Township where three-quarters of the Rohingya population has fled and most villages and all three camps for displaced people have been burned to the ground.

The United Nations' humanitarian office said that the number of Rohingya Muslims fleeing to Bangladesh since 25 August has topped 500,000. UN deputy spokesman Farhan Haq called it “the largest mass refugee movement in the region in decades.”

Rohingya crisis: Muslim village burnt to the ground

Bangladesh was already hosting thousands of Rohingya, and Haq said there are now believed to be “well over 700,000” Rohingya in the country.

“The failure to address this systematic violence could result in a spillover into central Rakhine, where an additional 250,000 Muslims could potentially face displacement,” Mr Guterres warned.

Rohingya “are outnumbered by Rakhine communities, some of whom have engaged in violent acts of vigilantism against their Muslim neighbours,” he said.

Mr Guterres also expressed deep concern at “the current climate of antagonism” by Burma authorities toward the United Nations and humanitarian groups that provide desperately needed aid. In the past few days, he said, the government has said repeatedly that “it was not the time” for unhindered humanitarian access to resume.

“It is imperative that U.N. agencies and our non-governmental partners be granted immediate and safe access to all affected communities,” he said.

The UN and its humanitarian partners have received $36.4 million in aid — just under half of the $77 million that the UN called for in early September to address the Rohingya crisis. But he said that “the scale of the emergency has far surpassed initial projections and the needs are being revised” upward.

On the key issue of returning Rohingya to their homes, the secretary-general said, “The core of the problem is protracted statelessness and its associated discrimination.”

Mr Guterres said Burma has committed to using a 1993 framework agreed to by the foreign ministers of Burma and Bangladesh to facilitate returns, but he told the council this isn't sufficient.

“Notably, the framework does not refer to resolving the root cause of displacement,” he said. “And moreover, it requires documents that the fleeing Rohingya may not be able to provide.”

Mr Guterres said all refugees in Bangladesh should be registered as “a critical first step.” He said the Muslims of Rakhine state “should be granted nationality” and urged Burma's government to revise its citizenship legislation to ensure this.

In the interim, Mr Guterres said those who are not entitled to citizenship according to the present laws must be able to obtain “a legal status that allows them to lead a normal life, including freedom of movement and access to labour markets, education and health services.”