Villagers in Myanmar fought security forces with catapults and crossbows in the Ayeyarwady river delta region, with local media reporting that 20 lives were lost in the violence.
State television claimed three "terrorists" had been killed and two arrested at the village of Hlayswe, where the security forces were trying to nab a wanted man on Saturday.
Junta spokespersons refused to take calls from media which was trying to get their version on the violence that occurred at Kyonpyaw township.
Angry crowds set ablaze ASEAN flags in Mandalay after a meeting between junta leader Min Aung Hlaing and envoys from the bloc on Friday.
Clashes broke out before dawn on Saturday at Hlayswe, some 150 km northwest of the main city of Yangon, when soldiers said they had come to search for weapons, local media outlets and residents said.
"The people in the village only have crossbows and there are a lot of casualties on the people's side," a resident said on the condition of anonymity.
Khit Thit Media and the Delta News Agency said 20 civilians had been killed and more wounded.
They said villagers had tried to fight back with catapults after soldiers assaulted residents in what they said was a search for arms.
MRTV state television said security forces had come under attack with compressed air guns and darts. After the shootout, the bodies of three attackers had been found, it said.
If confirmed, the toll given by the local media would be the highest in one day in nearly two months.
Some 845 people had previously been killed by the army and police since the February 1 coup, according to an activist group. The junta challenges that figure as exaggerated.
It was some of the worst violence since the coup in the Ayeyarwady region, an important rice growing area that has large populations of both the Bamar majority ethnic group, from which much of the army is drawn, and the Karen minority.
Post-coup flareups have been reported from the borderlands where 25-30 ethnic rebel armies have been waging insurgencies for decades. The junta has also been faced by daily protests and paralysing strikes.
The anti-junta Shwegu People's Defence Force said it had attacked a police station in northern Shwegu late on Friday together with the Kachin Independence Army (KIA).
KIA claims heavy police casualties but did not specify how many.
In eastern Myanmar, the Mobye People's Defence Force said it had clashed with the army on Friday and claimed four soldiers had been killed.
Despite the turmoil, Myanmar's army has shown little sign of heeding calls from its opponents to relinquish its hold.
This week, the junta received its first high-profile foreign visitors - the head of the International Committee of the Red Cross and the two ASEAN envoys.
An underground opposition government set up by opponents of the junta said after the envoys' visit on Friday it had lost faith in ASEAN's attempts to end the crisis - the main international effort to resolve it.