Those in areas hit by fighting were in “urgent need” of food, water, shelter and health care, it said, adding that travel restrictions imposed by security forces were delaying the delivery of much-needed aid.
Locals in Kayah state have accused the military of using artillery shells that have landed in villages.
AFP images from the region have showed villagers manufacturing guns in makeshift factories as local defence groups go up against Myanmar’s battle-hardened military.
More than 800 people have been killed across the country in a brutal military crackdown on dissent since February, according to a local monitoring group.
Myanmar’s national economy and banking system have been paralysed since the army’s power grab.
Livelihoods have been lost after strikes and factory closures, fuel prices have shot up and those lucky enough to have bank savings face day-long queues to withdraw their cash.
On Tuesday the Red Cross said it was urgently ramping up efforts to meet the humanitarian needs of 236,000 people in Myanmar, already reeling from the Covid-19 pandemic before the coup struck.
The announcement came after the charity’s president Peter Maurer was granted a rare meeting with junta leader Min Aung Hlaing last week and called for increased humanitarian access to the country.