At least 6,700 Rohingya Muslims were killed in the month after violence broke out in Myanmar in August, according to a report published by NGO Medecins Sans Frontieres (MSF).
Based on surveys of refugees in Bangladesh, the number is much higher than Myanmar’s official figure of 400.
Nearly 730 children under the age of five were among the figures.
MSF said it was “the clearest indication yet of the widespread violence” by the Myanmar regime.
The Myanmar army has blamed the violence on “terrorists” and has denied any wrongdoing.
More than 647,000 Rohingya refugees have fled to Bangladesh since August, the MSF says.
Dr Sidney Wong, MSF’s medical director said: “The numbers of deaths are likely to be an underestimation, as we have not surveyed all refugee settlements in Bangladesh and because the surveys don’t account for the families who never made it out of Myanmar.”
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The majority of the people killed (69%) were shot, while others were burned and beaten to death.
“We heard reports of entire families who perished after they were locked inside their homes, while they were set alight,” Dr Wong said.
Some of the worst violence is believed to have occurred in Tula Toli, in a village in the town of Maungdaw, where survivors say residents were rounded up on riverbanks and shot as they tried to flee.
5Pillars have seen videos taken by Rohingya villagers showing the corpses of children washed up on shores.
Survivors believe thousands more may have died in that village alone.
The high death toll tallies with reports from numerous journalists and human rights groups.