The UN office in Myanmar estimates that 100,000 people are internally displaced in the eastern part of the country due to fighting between armed civilians and security forces.
The office on Tuesday expressed concern about "the rapidly deteriorating security and humanitarian situation in Kayah State" where violence is escalating between security forces and citizens who oppose military rule.
The office says security forces are indiscriminately attacking civilian areas, and that evacuees have fled to relatively safe areas and forests.
The UN calls for "all parties to urgently take the necessary measures and precautions to protect civilians" who have not joined the fighting.
It added that "people fleeing and those remaining in locations affected by ongoing hostilities are in urgent need of food, water, shelter, fuel and access to healthcare."
The UN calls on security forces "to allow safe passage of humanitarian supplies and personnel."