The recent flare up in Myanmar's Shan State comes as an outgoing military-backed government prepares to hand over power to a civilian government led by Aung San Suu Kyi's National League for Democracy.
Shan, a large and hilly province on Myanmar's eastern border, has hosted multiple insurgencies over the decades by ethnic minorities fighting for greater autonomy or independence.
The latest fighting has pitted the military against the Ta'ang National Liberation Army (TNLA).
The TNLA are one of a handful of rebel groups who have yet to sign up to a broad ceasefire agreement that the military has been pushing.
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Suu Kyi has said bringing peace to Myanmar's border areas, where a variety of ethnic minority rebels have long fought insurgencies against central government rule, will be a priority of her new administration.
Witnesses described how they had fled Myanmar's military.
He said men were particularly afraid of being press ganged into service as porters or guides by Myanmar's army, which has long been accused of rights abuses.
A spokesman from the TNLA confirmed fighting had increased over the last two weeks with Myanmar's military using jets and helicopters.
"We have made contact with the Myanmar army about 25 times already this month. This month fighting is the most serious fighting in years. The situation is really tense between us," Major Mai Aik Kyaw told AFP.