DHAKA/YANGON - The United Nations appealed Thursday for massive help for nearly 400,000 Muslims from Myanmar who have fled to Bangladesh, with concern growing that the number could keep rising, unless Myanmar ends what critics denounce as “ethnic cleansing”.

The Rohingya are fleeing from a Myanmar military offensive in the western state of Rakhine that was triggered by a series of guerrilla attacks on Aug. 25 on security posts and an army camp in which about a dozen people were killed.

The United Nations has called for a massive intensification of relief operations to help the refugees, and a much bigger response from the international community.  “We urge the international community to step up humanitarian support and come up with help,” Mohammed Abdiker, director of operations and emergencies for the International Organisation for Migration, told a news conference in the Bangladeshi capital. The need was “massive”, he added.

UN Secretary-General Antonio Guterres and the UN Security Council on Wednesday urged Myanmar to end the violence, which he said was best described as ethnic cleansing. The government of Buddhist-majority Myanmar rejects such accusations, saying it is targeting “terrorists”.

Numerous Rohingya villages in the north of Rakhine have been torched but authorities have denied that security forces or Buddhist civilians set the fires. They blame the insurgents, and say 30,000 non-Muslim villagers were also displaced.

Smoke was rising from at least five places on the Myanmar side of the border on Thursday, a Reuters reporter in Bangladesh said. It was not clear what was burning or who set the fires.

The crisis has raised questions about Suu Kyi’s commitment to human rights, and could strain relations with Western backers supporting her leadership of Myanmar’s transition from decades of strict military rule and economic isolation. Critics have called for her to be stripped of her Nobel prize for failing to do more to halt the strife, though national security remains firmly in the hands of the military.

Rohingya militants, whose raids in western Myanmar provoked an army crackdown that spurred a humanitarian crisis, denied any links to global terror groups, days after Al-Qaeda urged Muslims to rally to their cause. The Arakan Rohingya Salvation Army (ARSA) says it is trying to defend the minority group from a long campaign of persecution in Buddhist-majority Myanmar, where the Rohingya are denied citizenship.

ARSA has repeatedly distanced itself from the agenda of international jihad, instead insisting its claims are local and in defence of major state repression. "ARSA feels that it is necessary to make it clear that it has no links with Al Qaeda, the Islamic State in Iraq and Syria (ISIS), Lashkar-e-Taiba or any transnational terrorist group," the group said in a statement posted on its Twitter account. "We do not welcome the involvement of these groups in the Arakan (Rakhine) conflict. ARSA calls on states in the region to intercept and prevent terrorists from entering Arakan and making a bad situation worse."

According to the International Crisis group, ARSA is steered by Rohingya emigres in Saudi Arabia and commanded in the field by overseas-trained guerilla fighters. But most of its recruits are armed with crude weapons like machetes and sticks.

US Secretary of State Rex Tillerson also condemned violence against Rohingya Muslims in Myanmar as "unacceptable", as thousands of refugees continue to stream across the border into Bangladesh. "We need to support Aung San Suu Kyi and her leadership but also be very clear and unequivocal to the military power sharing in that government that this is unacceptable," Tillerson said.

"This violence must stop. This persecution must stop. It has been characterised by many as ethnic cleansing. That must stop," he said during a visit to London, speaking alongside British counterpart Boris Johnson. "I think it is a defining moment in many ways for this new emerging democracy," Tillerson said, acknowledging that Myanmar's leader Suu Kyi found herself in a "difficult and complex situation".

European Commission President Jean-Claude Juncker Thursday condemned the crisis in Myanmar as a "shocking catastrophe", as the European Parliament demanded an immediate end to violence against Rohingya Muslims.

"What is happening in Myanmar is a shocking catastrophe really, because once again people are trying to eradicate whole ethnic groups," Juncker said during a question and answer session with a young YouTube star. "Europe is in the process of seeing with the Myanmar government and neighbouring countries in what way we can be useful."

Juncker however declined to say whether Suu Kyi should be stripped of the Nobel Peace Prize, an award the EU itself won in 2012. Euro-MPs meeting in Strasbourg, France, passed a resolution urging Suu Kyi to "condemn unequivocally" all incitement to racial and religious hatred. The European Parliament resolution "strongly urges the military and security forces to immediately cease the killings, harassment and rape of the Rohingya people, and the burning of their homes".

The Indian government Thursday told the Supreme Court that Rohingya refugees were “a threat to national security”, pushing back against condemnation of its plans to deport them.  India’s top court is hearing a challenge to Prime Minister Narendra Modi’s government’s decision to deport Rohingya Muslims, filed by two Rohingyas living in Delhi who fled from Myanmarbout six years ago. Some groups allied to Modi’s Bharatiya Janata Party have stepped up calls for Rohingyas to leave, and Modi said last week that India shared Myanmar’s concerns about “extremist violence” in Rakhine state.