International aid group Doctors Without Borders said its field survey has found at least 6,700 Rohingya Muslims were killed between August and September in a crackdown by Burma's security forces.

The group, known by the acronym from its French name, MSF, said in a statement made available Thursday that it had conducted the survey in refugee camps in Bangladesh, and estimated that at least 6,700 Rohingya died in Burma's Rakhine state between 25 August and 24 September.

About 630,000 Rohingya have fled Burma into Bangladesh to escape what the United Nations has called “ethnic cleansing”.

The estimate of the number of deaths announced by the group compares to Burma's government figure of 400 in September as a result of attacks on police posts by Rohingya militants.

According to MSF, the dead included at least 730 children younger than five. Burma's Information Ministry had said that most of the 400 dead were “extremist terrorists” who died during the military's “clearance operations.”

International aid and rights groups have accused the military of arson, killings and rapes of Rohingya villagers. Burmese authorities blamed Rohingya militants for the violence.

Though more than 1 million ethnic Rohingya Muslims have lived in the country for generations, they were stripped of their citizenship, denied almost all rights and labelled stateless.

“The peak in deaths coincides with the launch of the latest 'clearance operations' by Burma security forces in the last week of August,” MSF Medical director, Sidney Wong, in a statement.

Bullets and burns: injured Rohingya refugees Show all 10 1 /10 Bullets and burns: injured Rohingya refugees Bullets and burns: injured Rohingya refugees Rohingya refugee Mohamed Jabair, 21, reveals the burns on his bod, which he said he sustained when his house was set on fire in Myanmar REUTERS/Jorge Silva Bullets and burns: injured Rohingya refugees Refugee Momtaz Begum, 30, at Balukhali refugee camp. Begum told how soldiers came to her village demanding valuables.After beating her, they locked her inside her house and set the roof on fire. She escaped to find her three sons dead and her daughter beaten and bleeding REUTERS/Jorge Silva Bullets and burns: injured Rohingya refugees Imam Hossain, 42, sleeps at Kutupalang refugee camp, near Cox's Bazar. Hossain said he was returning home after teaching at a madrassa in his village when three men attacked him with knives REUTERS/Jorge Silva Bullets and burns: injured Rohingya refugees Rohingya refugee Setara Begum, 12, at Nayapara refugee camp. The home of Begum and her siblings was hit by a rocket. The young girl received no treatment for the severe burns to her feet. Her feet healed but she has no toes. Her mother said: 'She has been mute from that day, and doesn't speak to anyone. She only cries silently' REUTERS/Jorge Silva Bullets and burns: injured Rohingya refugees Mohamed Heron, 6, and his brother Mohamed Akter, 4, show the burns on their bodies at Kutupalong refugee camp. The boys' uncle said the burns resulted from Myanmar's armed forces firing rockets at their village Reuters Bullets and burns: injured Rohingya refugees Kalabarow, 50, at Leda refugee camp, in Bangladesh. Kalabarow said her husband, daughter and son were killed when soldiers fired on her village in Maungdaw. She was hit and lay on the floor pretending to be dead for several hours before a grandson found her. During their journey to Bangladesh, a village doctor amputated her REUTERS/Jorge Silva Bullets and burns: injured Rohingya refugees Ansar Allah, 11, at Leda refugee camp in Bangladesh. Allah showed a large scar – the result of a gunshot wound. His mother Samara said: 'They sprayed us with bullets, as our house was burning' REUTERS/Jorge Silva Bullets and burns: injured Rohingya refugees Anwara Begum, 36, at Kutupalang refugee camp, near Cox's Bazar. Begum said she woke to find her home in Maungdaw township in flames REUTERS/Jorge Silva Bullets and burns: injured Rohingya refugees Abdu Rahaman, 73, at Leda refugee camp in Bangladesh. Rahaman, a merchant from Maungdaw, was ambushed while walking on a mountain path with other refugees. A machete thrown at his feet severed three toes REUTERS/Jorge Silva Bullets and burns: injured Rohingya refugees Nur Kamal, 17, described how soldiers assaulted him after they found him hiding in his home in Maungdaw. His uncle found him unconscious in a pool of blood. It took them two weeks to get to Bangladesh. Kamal said: 'We want the international community to help us obtain justice' REUTERS

She said the findings were staggering, both in terms of the numbers of people who reported a family member dead as a result of violence, and horrific ways in which they said they were killed or severely injured.

MSF said that among children below the age of five, more than 59 per cent who were killed during that period were reportedly shot, 15 per cent burnt to death in their homes, 7 per cent beaten to death and 2 per cent died due to land mine blasts.

Since the Burma's military conducted operations against the Rohingya in northern Rakhine state, the civilian government has barred most journalists, international observers and humanitarian aid workers from independently travelling to the region.

MSF said the numbers of deaths are likely to be an underestimation “as we have not surveyed all refugee resettlements in Bangladesh because the surveys don't account for the families who never made it out of Burma”.