Reports from Burma say some 300 government troops have attacked ethnic Karen rebels near the border with Thailand.
The Karen National Union told the Reuters news agency that five Burmese soldiers were killed in the fighting, which forced the villagers in the area to flee their homes.
The Thai News Agency reports that some villagers in Thailand also evacuated to escape the fighting. There has been no comment from the Burmese military government.
The Karen National Union, which has been fighting for autonomy in eastern Burma for decades, is the only major ethnic rebel group that has not signed a formal ceasefire with the Burmese government.
Information for this report is provided by Reuters.