Dozens of Myanmar security force members were killed Sunday, rebel fighters said, after heavy fighting in the coup-hit country's eastern fringe.

Myanmar has been in chaos since the February putsch, as the military uses lethal force to crack down on dissent.

The civilian death toll has climbed to at least 815 people, according to a local monitoring group.

The violence has pushed some in the anti-junta movement to form a so-called "People's Defence Force" (PDF) in their own townships -- made up of civilians who fight back against security forces with homemade weapons.

There were clashes in eastern Myanmar over the weekend, particularly in Kayah state's Demoso town, and in neighbouring Shan state.

People's Defence Force member Thet Wai -- not his real name -- said at least 20 police officers died Sunday and his side seized a police station in Moebyel town, Shan state, east of the capital Naypyidaw.

The police station was burnt down and rebel fighters also took four security force members into custody, local media reported.

"I thought today is a day of conquest," Thet Wai, 29, told AFP.

"But I am also worried because we have seen air strikes and tanks today. They have much better weapons than us."

He said the Myanmar military had launched helicopter air strikes in the evening at Demoso, a town in Kayah state about 40 kilometres south.

Another civilian fighter at Demoso said at least 13 Myanmar soldiers had been killed Sunday, while four of his men were wounded.

"We intended to seize their police station, but they used air strikes and we could not stop their reinforcement trucks getting into the town," he said.

"We had to withdraw our troops from fighting."

The fighting continued through Sunday night, according to a senior leader of the Karenni National Progressive Party -- an ethnic armed group with a stronghold in Kayah state.

He confirmed that the military was using tanks, helicopters and mortar attacks in Demoso and Loikaw, the capital of Kayah state.

© AFP