Seoul (AFP) - 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 164,000 mostly Rohingya civilians have fled to Bangladesh, overwhelming refugee camps that were already bursting at the seams.

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.

The figures given by Lee, a South Korean academic, 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 Lee told AFP that 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.

In an interview at Sungkyunkwan University in Seoul, where she is a professor in the department of child psychology and education, she told AFP she feared "it's going to be one of the worst disasters that the world and Myanmar has seen in recent years".

- 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.

"She needs to step up," Lee said, and "show the world what she has really fought to achieve was a free and democratic Myanmar".

"She really needs to show more compassion to all of the people in Myanmar."

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.

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.

"If the political price of your ascension to the highest office in Myanmar is your silence, the price is surely too steep."

Under the Nobel prize statutes awards cannot be revoked, but Lee said the laureates' statements showed "how grave the situation is".

The Myanmar military are controlled by commander in chief Min Aung Hlaing but Suu Kyi should speak out and try to convince him to end the violence, she added. "This is where her leadership comes."

But 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."