US President Donald Trump wants the UN Security Council to take "strong and swift action" to end violence against Myanmar's Rohingya.

Speaking at a Security Council meeting on peacekeeping reform, Vice President Mike Pence accused the Myanmar military of responding to attacks on government outposts "with terrible savagery, burning villages, driving the Rohingya from their homes".

Pence repeated a US call for the Myanmar military to end the violence and support diplomatic efforts for a long-term solution for the majority-Muslim Rohingya, who are denied citizenship in a country where many Buddhists regard them as illegal immigrants.

"President Trump and I also call on the Security Council of the United States to take strong and swift action to bring this crisis to an end and bring hope and help to the Rohingya people in their hour of need," he told the 15-member council.

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The security council has met twice behind closed doors since the crisis began on August 25, and last week issued an informal statement to the press condemning the situation and urging Myanmar authorities to end the violence.

"Unless this violence is stopped, which justice demands, it will only get worse. And it will sow seeds of hatred and chaos that may well consume the region for generations to come and threaten the peace of us all," Pence said.

It was the strongest US government response yet to the violence in Myanmar's Rakhine state that has forced more than 420,000 Rohingya into Bangladesh, fleeing a military offensive the United Nations has branded ethnic cleansing.

French President Emmanuel Macron earlier Wednesday described the military's campaign as "genocide".

Myanmar insisted in the UN that the crisis in Rakhine was easing, after heavy international criticism.

Myanmar's Second Vice President Henry Van Thio addressed the annual UN General Assembly in place of leader Aung San Suu Kyi, who a day earlier delivered a speech calling for patience.

Van Thio's remarks are even less likely than Aung San Suu Kyi's to mollify global concerns, as he questioned the reasons for the flight of members of the Rohingya ethnic minority.

"I am happy to inform you that the situation has improved," Van Thio said in his address, saying there have been no clashes since September 5.

"Accordingly, we are concerned by reports that the numbers of Muslims crossing into Bangladesh remain unabated. We would need to find out the reason for this exodus," he said.

READ MORE: 'Traitor' - Rohingya react to Aung San Suu Kyi's speech

Van Thio did not use the term Rohingya, referring to them simply as Muslims. He noted the army campaign came in response to a rebel attack and said non-Muslims have also suffered.

Myanmar's third-in-command thanked foreign countries for their support, not referring directly to their criticism.

"Humanitarian assistance is our first priority. We are committed to ensuring that aid is received by all those in need, without discrimination," Van Thio said.

Aung San Suu Kyi's stance has disheartened human rights groups who had campaigned for her freedom during the Nobel Peace Prize winner's 15 years under house arrest by the ruling military government.

But analysts say Aung San Suu Kyi, while now the country's de facto leader, may not be able to curb the army even if she took the political risk of speaking out.