More than 1,000 Rohingya Muslims may have been killed in a Myanmar army crackdown, according to two senior United Nations officials dealing with refugees fleeing the violence, suggesting the death toll has been a far greater than previously reported.

The officials, from two separate U.N. agencies working in Bangladesh, where nearly 70,000 Rohingya have fled in recent months, said they were concerned the outside world had not fully grasped the severity of the crisis unfolding in Myanmar's Rakhine State.

"The talk until now has been of hundreds of deaths. This is probably an underestimation — we could be looking at thousands," said one of the officials, speaking on condition of anonymity. Both officials, in separate interviews, cited the weight of testimony gathered by their agencies from refugees over the past four months for concluding the death toll likely exceeded 1,000.