Fighting in northern Myanmar between government forces and the rebel Kachin Independence Army, or KIA, has forced more than 4,000 people to flee their homes.
Col Naw Bu, a KIA spokesman, said the fighting will become "more intense" because the army is sending more troops to the area.
Aid organizations have requested access to the clash-stricken, remote northeastern area near the country's border with China. Charities fear thousands of vulnerable people remain trapped since the fighting escalated in April.
"Our biggest concern is for the safety of civilians, including pregnant women, the elderly, small children and people with disabilities," Mark Cutts, the head of the U.N.'s Office for the Coordination of Humanitarian Affairs told the French news agency. "We must ensure these people are protected."
Elsewhere in Myanmar, envoys from the U.N. Security Council are expected Monday after visiting Bangladesh's Cox's Bazar where Rohingya Muslims fled after military-led violence erupted around their homes in Myanmar.
The delegation arrived in Bangladesh Saturday for a first-hand look at the situation of the Rohingya. The U.N. envoys will meet with Bangladesh Prime Minister Sheikh Hasina before leaving for Myanmar where they will visit Rakhine State and meet with de facto leader Aung San Suu Kyi.
Nearly 700,000 Rohingyas left Myanmar's Rakhine State after the violence started in late August 2017.
Myanmar denies accusations of ethnic cleansing.
Rohingyas in Myanmar have been denied citizenship even though many of their families have lived in Myanmar for generations.