Pressure grew on Myanmar on Monday as a rights group urged world leaders to impose sanctions on its military, which is accused of driving out more than 410,000 Rohingya Muslims in an orchestrated “ethnic cleansing” campaign.

The call from Human Rights Watch came as the UN General Assembly prepared to convene in New York, with the crisis in Myanmar high on the agenda.

It also came on the eve of a highly-anticipated national address Tuesday by Myanmar's civilian leader Aung San Suu Kyi, her first on the crisis in Rakhine state.

The exodus of Rohingya refugees from mainly Buddhist Myanmar to neighbouring Bangladesh has sparked a humanitarian emergency. Aid groups are struggling to provide relief to a daily stream of new arrivals, more than half of whom are children.

The number also includes 70,000 pregnant or breastfeeding women, according to Bangladesh'sinformation minister Hasanul Haq.

Myanmar has suggested it will not take back all who had fled across the border, accusing them of links to the Rohingya militants whose raids on police posts in August triggered the army backlash.

Any clear moves to block the refugees' return will likely anger Bangladesh Prime Minister Sheik Hasina. She will use the General Assembly to press Myanmar to take back all the Rohingya massing in shanty towns and camps in Bangladesh near the border.

Human Rights Watch also called for the “safe and voluntary return” of the displaced as it urged governments around the globe to punish Myanmar's army with sanctions for the “ongoing atrocities” against the Rohingya.

“The United Nations Security Council and concerned countries should impose targeted sanctions and an arms embargo on the Burmese military to end its ethnic cleansing campaign against Rohingya Muslims,” the group said in a statement.

Myanmar's military was hit with Western sanctions during its 50-year rule of the country. But most have been lifted in recent years as the generals have allowed a partial transition to democracy.

“Burma's senior military commanders are more likely to heed the calls of the international community if they are suffering real economic consequences,” said John Sifton, HRW's Asia advocacy director.

Suu Kyi's 'last chance'

Nobel peace laureate Suu Kyi has shocked the international community with her near-silence on the plight of the Rohingya and her failure to condemn the actions of the army, with whom she has a delicate power-sharing arrangement.

Speaking to the BBC over the weekend, UN Secretary General Antonio Guterres said Suu Kyi had a “last chance” to stop the humanitarian calamity.

But analysts say it will be difficult for her to appease both global outrage and combustible religious tensions at home, where there is broad support among the mainly Buddhist population for the army's crackdown.

“I'm worried that there is almost no possibility given the political climate in Myanmar for balancing the expectations of most of the country and the expectations of the international community,” Richard Horsey, an independent analyst based in Myanmar, told AFP.

Duelling protests

The sharp divide was on display Monday as protests broke out in Dhaka ─ where 20,000 Islamist hardliners marched in solidarity with the Rohingya ─ and in Yangon, where a group of 300 gathered to blast global interference in the conflict.

While the world has watched with horror, there is little sympathy for the Rohingya inside Myanmar.

Many Buddhists revile the Muslim minority and have long denied their existence as an ethnic group, insisting they are illegal immigrants from Bangladesh.

Suu Kyi's government has so far defended the military campaign as a legitimate crackdown on the Rohingya militants, who first emerged as a fighting force last October.

On Sunday Myanmar's Information Committee accused those who fled to Bangladesh ─ more than a third of the Rohingya population ─ of working in cahoots with the Rohingya militants, a rag-tag group of fighters armed with mostly rudimentary weapons.

“Those who fled the villages made their way to the other country for fear of being arrested as they got involved in the violent attacks,” the statement said.

“Legal protection will be given to the villages whose residents did not flee,” it added.

The violence has gutted large swathes of northern Rakhine in just over three weeks, with fires visible almost daily across the border from the Bangladesh camps.

Some 30,000 ethnic Rakhine Buddhists and Hindus have also been displaced by unrest in northern Rakhine, where foreign aid has been severely curtailed.

On Monday, Doctors Without Borders repeated calls for “unfettered access” to the conflict zone, saying hundreds of thousands of people are thought to be languishing “without any meaningful form of humanitarian assistance”.