BANGKOK (AP) — International aid group Doctors Without Borders says its field survey has found at least 6,700 Rohingya Muslims were killed between August and September in a crackdown by Myanmar's security forces.

The group, known by its French acronym MSF, says the survey it conducted in refugee camps in Bangladesh estimated that at least 9,000 Rohingya died in Myanmar's Rakhine state between Aug. 25 and Sept. 24. About 630,000 Rohingya have fled Myanmar 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 Myanmar's government figure of 400 in September as a result of attacks on police posts by Rohingya militants.

MSF says the dead included at least 730 children younger than 5.