At least 6,700 Rohingya Muslims were killed in the first month of a Myanmar army crackdown on rebels in Rakhine state that began in late August, Doctors Without Borders (MSF) said on Thursday.

"At least 6,700 Rohingya, in the most conservative estimations, are estimated to have been killed, including at least 730 children below the age of five years," the aid group said, basing the figures on surveys it had conducted.