The United Nations Security Council and the UN Secretary-General Antonio Guterres have urged Myanmar to end the violence against Rohingya Muslims.
Around 370,000 people have escaped into neighbouring Bangladesh following the latest unrest which broke out on August 25 when Rohingya fighters attacked police posts.
Guterres said the situation in Myanmar's western state of Rakhine can be described as ethnic cleansing.
"When one-third of the Rohingya population had to flee the country, could you find a better word to describe it?" he told a news conference.
"I call on the Myanmar authorities to suspend military action, end the violence, uphold the rule of law, and recognize the right of return of all those who had to leave the country," said Guterres, adding that he had spoken several times with Myanmar's de facto leader, Aung San Suu Kyi.
The 15-member Security Council met behind closed doors, at the request of Sweden and Britain, to discuss the crisis for the second time since it began.
The council "expressed concern about reports of excessive violence during the security operations and called for immediate steps to end the violence in Rakhine, de-escalate the situation, re-establish law and order, ensure the protection of civilians ... and resolve the refugee problem."
The British Ambassador to the U.N. Matthew Rycroft said it was the first statement from the Security Council on Myanmar in nine years.
Suu Kyi has cancelled her trip to next week's U.N. General Assembly to deal with the crisis
She is due to give her first speech on the situation in a televised address in the coming days.
Suu Kyi has been widely condemned for her inaction in the face of the crisis, denting the Nobel peace laureate's reputation.
The Secretary-General also said he has spoken to Suu Kyi several times.
"The humanitarian situation is catastrophic," Guterres said. "This is a dramatic tragedy. People are dying and suffering in horrible numbers and we need to stop it."
On the border separating Bangladesh from Myanmar, thousands of Rohingya Muslim families remain in limbo after escaping from the threat of attack.
Between 8,000 to 10,000 are still camped outside the danger zone.
The Myanmar government says about 400 people have been killed in the latest fighting in Rakhine.
Bangladeshi security forces have instructions to not let them in, said Monzurul Hassan Khan, a border guard officer.
Some Rohingyas say although they are afraid to return, they are not ready to abandon their homes altogether and become refugees in Bangladesh.
“I can see my house but can’t go there,” said Syed Karim, whose Myanmar village could be seen from his shack in the no-man’s land.
“In our country, Buddha worshippers treat us like a virus that needs to be eliminated. We have heard them saying, ‘No Rohingya in Myanmar.’ But we will go back,” Arif said.