The UN has announced it will investigate reports of mass killings, torture, sexual violence, and the burning of Rohingya villages in Burma.

At least 400,000 people are believed to have fled over the border into Bangladesh to escape widespread rape, murder and the destruction of whole villages in the western state of Rakhine by the Burmese military and mobs from the country's Buddhist-majority population.

Desperate refugees have reportedly been seen climbing over wire border fences in an attempt to escape and the Burmese military are reportedly laying land mines to ensure they do not return.

One fleeing Rohingya told reporters that ethnic Rakhine Buddhists came to the villages and shouted: "leave or we will kill you all".

The Rohingya, who are predominately Muslim, have faced persecution in Burma for decades but there has been a fresh upsurge in violence against them since 25 August after a small group of Islamist militants attacked 30 police stations and a military base.

The UN has previously said the violence was a "textbook example of ethnic cleansing" and urged the Burmese military to end operations in the region, grant access to humanitarian groups and commit to aiding the safe return of civilians to their homes.

The chairman of the fact-finding mission, Marzuki Darusman asked the Human Rights Council for a further six months to investigate the violence – taking it up to September 2018.

In pictures: Rohinga refugees in Bangladesh Show all 12 1 /12 In pictures: Rohinga refugees in Bangladesh In pictures: Rohinga refugees in Bangladesh Bangladesh Hamid and his daughter Rajama sit inside their home in the Shamalapur Rohingya refugee settlement in Chittagong district. They fled to Bangladesh from the Dhuachopara village in the Rachidhong district of Myanmar In pictures: Rohinga refugees in Bangladesh Bangladesh Rajama sits in the doorway of her home in the Shamalapur Rohingya refugee settlement in Chittagong district, Bangladesh. She fled to Bangladesh from the Dhuachopara village in the Rachidhong district of Myanmar. The Chakma people came during prayer time in a giant mob and started burning houses and burning people alive. They beat her father and brother, and then they opened fired and started shooting and killing people at random. A group of people fled to the mosque and the Chakma followed, opening fire inside. Her father fled to the ocean and escaped to Bangladesh by boat. Rajama came to Bangladesh 3 days after the riot to find her father. When she arrived in the port of Teknaf the dock workers held her captive for 3 days with no food or water. They beat her and abused her before letting her go. She has 7 siblings back in Myanmar who were not able to escape. 'I miss my family, but how can I miss them? I want to live.' she says In pictures: Rohinga refugees in Bangladesh Bangladesh 60 year old Mukluhammad, 25 year old Zahad Hossain, and 45 year old Dilchar build a roof on their new home in the Shamalapur Rohingya refugee settlement in Chittagong district In pictures: Rohinga refugees in Bangladesh Bangladesh Rohingya refugees unload fish from a boat in the Shamalapur Rohingya refugee settlement in Chittagong district In pictures: Rohinga refugees in Bangladesh Bangladesh People push a boat to land in the Shamalapur Rohingya refugee settlement in Chittagong district In pictures: Rohinga refugees in Bangladesh Bangladesh 32 year old Mahada Khatum repairs a fishing net outside her home in the Shamalapur Rohingya refugee settlement in Chittagong district. Some years ago she escaped violence and discrimination from the Zomgara Baharchara village in the Meherulla district of Myanmar In pictures: Rohinga refugees in Bangladesh Bangladesh A Rohingya child is seen in a home in the Shamalapur Rohingya refugee settlement in Chittagong district. Tomas Ojea Quintana, the UN special rapporteur on Human Rights, said that recent developments in Myanmar's Rakhine state were the latest in a 'long history of discrimination and persecution against the Rohingya Muslim community which could amount to crimes against humanity', and that the Myanmar government's decision not to allow Rohingya Muslims to register their ethnicity in the March census meant that the population tally was not in accordance with international standards In pictures: Rohinga refugees in Bangladesh Bangladesh 7 year old Shumiakter helps her 5 year old sister Rubiata swing on a rope outside their home in the Shamalapur Rohingya refugee settlement in Chittagong district. After their grandparents were killed in the sectarian violence in Myanmar their parents fled to Bangladesh In pictures: Rohinga refugees in Bangladesh Bangladesh 32 year old Mahada Khatum, 5 year old Hasan Sharif, and 9 year old Umma Kulsum sit outside their home in the Shamalapur Rohingya refugee settlement in Chittagong district. The family escaped violence and discrimination from the Zomgara Baharchara village in the Meherulla district of Myanmar In pictures: Rohinga refugees in Bangladesh Bangladesh 45 year old Dilbhar looks towards the camera as she stands in the Shamalapur Rohingya refugee settlement in Chittagong district. She escaped to Bangladesh from the Bodchara village in the Mondu district of Myanmar In pictures: Rohinga refugees in Bangladesh Bangladesh Over the years hundreds of thousands of Rohingya refugees have taken refuge in Bangladesh to escape the deadly sectarian violence In pictures: Rohinga refugees in Bangladesh Bangladesh 12 year old Nurana stands outside her home in the Shamalapur Rohingya refugee settlement in Chittagong district. She escaped to Bangladesh from Myanmar with her parents and 6 siblings

He said the team "will go where the evidence leads us" but warned that he still needs a clear signal from the Burmese government that they will be allowed into the country.

He also called for the Burmese government to release its own investigation in the violence in Rakhine state which was completed in August.

But the Burmese ambassador to the UN, Htin Lynn, said the investigation was "not a helpful course of action" and said Burma was taking proportionate security measures against terrorists to restore peace.

Although there has been a small upswing in militant activity among the Rohingya in recent years, the overwhelming majority of the population has remained peaceful in spite of the violence against them.

The Burmese government officially claims the Rohingya are illegal immigrants from Bangladesh but the community can trace back its roots in Burma for centuries.

They are denied full citizenship, have little access to healthcare or education and their movements are strictly controlled by the military.

She invited diplomats to visit Rakhine to see for themselves what was going on and claimed that "more than half" of Rohingya villages remained intact.