Rohingya Muslims in Myanmar are facing a catastrophic humanitarian situation, according to the UN secretary general.
Antonio Guterres said alleged attacks by security forces on Rohingya villagers were completely unacceptable. The army says it is fighting militants and denies targeting civilians.
Later the UN Security Council called for urgent steps to end the violence.
Some 379,000 Rohingyas have fled to Bangladesh since violence began last month.Whole villages have burned down.
The Rohingya, a mostly Muslim minority in the Buddhist-majority Rakhine state, have long experienced persecution in Myanmar, which says they are illegal immigrants. They have lived in Myanmar, also known as Burma, for generations but are denied citizenship.
But Myanmar officials say the country's de facto leader, Aung San Suu Kyi, will miss a key debate next week in the UN General Assembly.
She will, however, address the nation on TV on 19 September, the day the General Assembly meets. Officials said she would "speak for national reconciliation and peace".
Ms Suu Kyi has been criticised by former supporters in the West for failing to do enough to prevent the violence in Rakhine state.
Rohingya refugees say they have had no contact with any aid agencies or international aid bodies at all.
Many say they have had details from their basic identity papers - their names and the villages they are from - taken at the border. After that, they have been on their own.
What did the UN secretary general say?
The UN refugee agency says not enough aid is getting through to the Rohingya who have fled to Bangladesh.
Mr Guterres called on the international community to provide whatever assistance they could.
"The humanitarian situation it is catastrophic," he said.
"When we met last week there was 125,000 Rohingya refugees who had fled into Bangladesh. That number has now tripled to nearly 380,000.
"Many are staying in makeshift settlements or with those communities who are generously sharing what they have. But women and children are arriving hungry and malnourished."
He added that military action should also be suspended and those who had fled be allowed the right to return home.