António Guterres has urged the international community to help
The United Nations Secretary-General has reiterated his call for Muslims from Myanmar's Rakhine state to be granted nationality or a legal status.
António Guterres says such a status would allow them to lead "a normal life".
He has also urged the international community to help provide assistance for the nearly 380,000 people who have fled into Bangladesh.
"I call on the Myanmar authorities to suspend military action, end the violence, uphold the rule of law, and recognise the right of return of all those who had to leave the country," he said.
Mr Guterres repeated his call for "an effective action plan" to address the root causes of the situation, which he said he been left to fester for decades and has now escalated beyond Myanmar's borders, destabilising the region.
The UN Security Council is due to discuss the situation in an urgent closed-door meeting following an official letter from the Secretary-General expressing his concern.
"The humanitarian situation is catastrophic," he said.
"I urge all countries to do what they can for humanitarian assistance to be provided".
He also called on Myanmar authorities to ensure delivery of aid by UN agencies, non-governmental organisations and others.
The humanitarian community has this week launched a US$77m (€64m) appeal to aid some of the stateless refugees for the next three months.
It comes as the de-facto leader of Myanmar, Aung San Suu Kyi, has said she will not attend this month's UN General Assembly.
The Nobel Peace Prize winner has faced mounting international criticism over her response to the crisis.
Police and army in Myanmar - also known as Burma - have launched a violent crackdown in the state following attacks by Rohingya insurgents on police posts last month.
It is claimed that thousands of people in Rakhine state have been killed or tortured by security forces in recent weeks, with hundreds of thousands of refugees fleeing to neighbouring Bangladesh as a result.