Myanmar leader Aung San Suu Kyi will not attend the United Nations General Assembly later this month, her spokesman said on Wednesday, as the Nobel laureate faces a barrage of criticism over her failure to speak up for Rohingya Muslims fleeing Rakhine state in huge numbers.

A crackdown by Myanmar's army, launched in response to Rohingya militant attacks on August 25, has sent some 370,000 Rohingya refugees scrambling across the border to Bangladesh in less than three weeks. The violence has incubated a humanitarian crisis on both sides of the border.

Bangladesh is struggling to provide relief for exhausted and hungry refugees — some 60 per cent of whom are children — while nearly 30,000 ethnic Rakhine Buddhists as well as Hindus have been displaced inside Myanmar.

UN human rights chief, Zeid Ra'ad Al Hussein, accused Myanmar of waging a “systematic attack” on the Muslim Rohingya minority and warned that “ethnic cleansing” seemed to be under way.

Suu Kyi, Myanmar's first civilian leader in decades, does not control the actions of the powerful military, which ran the country for 50 years before allowing free elections in 2015.

There is also scant sympathy among Myanmar's Buddhist majority for the Rohingya, a stateless Muslim group branded 'Bengalis' — shorthand for illegal immigrants. But outside of her country Suu Kyi's reputation as a rights defender is in ruins over the Rohingya crisis.

Rights groups have pilloried the former democracy activist for failing to condemn the army campaign, which has left hundreds dead. Rohingya refugees have told chilling accounts of soldiers and firing on civilians and razing entire villages in northern Rakhine state with the help of Buddhist mobs.

The army denies allegations, while Suu Kyi has also played down claims of atrocities instead blaming “a huge iceberg of misinformation” for complicating the conflict.

“The state counsellor won't attend the meeting of the United Nations General Assembly,” said government spokesman Zaw Htay, using Suu Kyi's formal title. The spokesman did not explain the decision but said the country's Vice President Henry Van Thio would attend the summit, which runs through next week.

The UN's National Security Council also plans to meet behind closed doors on Wednesday to discuss the crisis, although China has indicated it will shoot down any attempt to censure its strategically pivotal Southeast Asian ally.

Fallen star

Suu Kyi, a Nobel Peace Prize winner garlanded for her dignified and defiant democracy activism under Myanmar's former junta, was once the darling of the international community.

She made her debut before the UN assembly last September, winning warm applause for a speech delivered months after she became Myanmar's first civilian leader in decades. In it, she vowed to find a solution to long-running ethnic and religious hatreds in Rakhine “that will lead to peace, stability and development for all communities within the state.”

In a sign of how far her star has fallen since, she has been blasted by the same rights groups that campaigned for her release from house arrest for failing to speak up in defence of the Rohingya.

Sympathisers say her hands are tied by the army, which still runs a chunk of the government and has complete control over all security matters. But fellow Nobel laureates have lined up to condemn her silence, with Archbishop Desmond Tutu calling it “incongruous for a symbol of righteousness to lead such a country.”

Denied citizenship by Myanmar, the Rohingya are loathed in Buddhist-majority Myanmar and unwanted by Bangladesh, which is providing temporary shelter to the refugees.

The US and other Western powers have rebuked the military campaign. But ahead of the UN Security Council meeting, Beijing on Tuesday offered Myanmar support saying the country was entitled to “safeguard” its stability.