More than 1,000 people may already have been killed in Myanmar, mostly minority Rohingya Muslims -- more than twice the government's total -- a senior United Nations representative told AFP on Friday, urging Aung San Suu Kyi to speak out.

In the last two weeks alone 270,000 mostly Rohingya civilians have fled to Bangladesh, overwhelming refugee camps that were already bursting at the seams, the UN said.

Others have died trying to flee the fighting in Rakhine state, where witnesses say entire villages have been burned since Rohingya militants launched a series of coordinated attacks on August 25, prompting a military-led crackdown.

On the basis of witness testimonies and the pattern of previous outbreaks of violence, said Yanghee Lee, the UN special rapporteur on human rights in Myanmar, "perhaps about a thousand or more are already dead".

"This might be from both sides but it would be heavily concentrated on the Rohingya population."

The Rohingya have long been subjected to discrimination in mostly Buddhist Myanmar, which denies them citizenship and regards them as illegal immigrants from Bangladesh, even if they have lived in the country for generations.

Bangladesh has struggled to cope with the latest influx, which takes the number of Rohingya refugees in the squalid refugee camps on its border with Myanmar to around 670,000.

The UN, which previously put the number of arrivals at 164,000, said the overnight leap was because of a more thorough assessment in areas not previously included in its counting.

But it also said there was a sharp increase in arrivals on Wednesday, when at least 300 boats from Myanmar landed in Bangladesh.

Scores of Rohingya have drowned trying to make the perilous sea journey in boats that the Bangladesh authorities say are woefully inadequate at this time of year, when the sea is rough.

Many of the dead were children unable to swim to safety.

- Worst disaster in years -

Lee, a South Korean academic, told AFP she feared "it's going to be one of the worst disasters that the world and Myanmar has seen in recent years".

The figures she gave are far higher than official tolls, which total 432.

Myanmar's army has previously said it has killed 387 Rohingya militants. Authorities say they have lost 15 security personnel since the August attacks.

In updated figures released by the authorities on Thursday, Myanmar said 6,600 Rohingya homes and 201 non-Muslim homes had been burned to the ground since August 25. 

They added some 30 civilians had been killed -- seven Rohingyas, seven Hindus and 16 Rakhine Buddhists -- in the fighting.

But in an interview at Sungkyunkwan University in Seoul, where she is a professor in the department of child psychology and education, Lee said it was "highly possible" the government had "underestimated numbers".

"The unfortunate thing, the serious thing is that we can't verify that now with no access."

Lee expressed scepticism about authorities' claims that the Rohingya were burning their own houses, pointing out that nearby Buddhist villages were untouched -- and it is the rainy season.

"If you have got people with guns and you're running away and it's damp, how easily can you set your own house on fire?" she asked.

- Forget the icon -

Myanmar's Nobel Peace Prize winner Aung San Suu Kyi, who spent years under house arrest when Myanmar was a military dictatorship, is now the country's de facto leader with the title of State Counsellor.

But she has so far failed to speak out on the violence, leaving her global reputation in tatters.

Rights groups, activists -- including many who campaigned for her in the past -- and her fellow Nobel laureates Malala Yousafzai and Archbishop Desmond Tutu have condemned her.

In a letter Tutu told his "dearly beloved younger sister" that "the images we are seeing of the suffering of the Rohingya fill us with pain and dread". 

"It is incongruous for a symbol of righteousness to lead such a country; it is adding to our pain," he added.

When it awarded Suu Kyi the 1991 Peace Prize the Nobel committee said that she "emphasises the need for conciliation between the sharply divided regions and ethnic groups in her country".

But earlier this week, in her first statement since the violence erupted, Suu Kyi, 72, condemned a "huge iceberg of misinformation" on the crisis, without mentioning the Rohingya flocking to Bangladesh.

Around 86 percent of Myanmar's population is Buddhist, Lee pointed out.

"What we forget is that she is a politician through and through. People expect her to have that big high moral voice but she's a politician, and what's the most important objective if you are a politician? Getting elected," she said.

"I think we need to delete our memories of the imprisoned democratic icon."