The international aid group Doctors Without Borders has released the first survey-based estimate of how many Rohingya were killed during the first and bloodiest month of a military crackdown that began Aug. 25 in Myanmar's Rakhine State.

The organization said that by its "most conservative estimates," 6,700 Rohingya were killed between Aug. 25 and Sept. 24, including 730 children under 5. Most are thought to have died from gunshot wounds, though some died in their burning homes and others after severe beatings. The figure does not include an estimated 2,300 Rohingya who died of nonviolent causes in that time frame, including starvation and drowning while attempting to flee.

The Burmese government's official estimate is 400, and it maintains that 376 of them were terrorists it targeted in "cleansing operations." The Rohingya are a mostly Muslim ethnic group that the Burmese government refuses to recognize as citizens, instead referring to them as Bengali, a term that implies that they are illegal immigrants from neighboring Bangladesh.

The United Nations and United States have both used the term "ethnic cleansing" to describe the violence in Myanmar since August. Myanmar strongly rejects the allegation.

Nearly 650,000 Rohingya — which represents well over half the number that lived in Myanmar, also called Burma, before the violence broke out — have now fled to Bangladesh, where they live in what are now the world's largest refugee camps.

Journalists and human rights groups have been largely restricted from working in Rakhine State, making a firsthand accounting of the ground situation difficult. Instead, most observers have relied on interviews and surveys among refugees now in Bangladesh. Reports have pointed to large-scale massacres, systematic rape and the burning and looting of hundreds of Rohingya villages — all by Burmese security forces and vigilantes belonging to local Buddhist populations.

Doctors Without Borders extrapolated the estimated death toll from surveys of 2,434 households now in refugee camps in Bangladesh.

"What we uncovered was staggering, both in terms of the numbers of people who reported a family member died as a result of violence, and the horrific ways in which they said they were killed or severely injured," said the group's medical director, Sidney Wong.

"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," Wong said.

The violence in August and September triggered the most rapid exodus of refugees since the genocidal killings in Rwanda in 1994. While military operations have gradually decreased in intensity over time, thousands of Rohingya continue to leave Myanmar seeking refuge in Bangladesh on a weekly basis.

The worst violence is believed to have occurred in Maungdaw township, a region closest to the Bangladesh border where for months the fires of burning villages were visible across a estuary dividing the two countries. Survivors from one Rohingya village, Tula Toli, say that thousands of people may have been killed there alone. They say soldiers rounded up residents along the village's riverbanks and summarily executed them.