Fighters opposed to Myanmar's military junta burned down a police station in the eastern town of Mobye on Sunday and said they killed at least 13 members of the security forces and captured four, local media said.
Videos shared on social media showed what appeared to be the bodies of security forces in the latest fighting of a general upsurge of conflict in parts of Myanmar since the Feb. 1 coup that overthrew elected leader Aung San Suu Kyi.
A gun battle also erupted near the Chinese border early on Sunday, while on Saturday an armed ethnic group opposed to the coup launched an attack on a jade mining town on the other side of Myanmar, near India.
Video from Mobye showed bodies in the uniforms of the security forces, while other pictures showed four men who were said to be police with their hands behind their backs and blindfolded with surgical masks.
A police vehicle was shown in flames as dozens of fighters milled at the scene.
Reuters was unable to reach a junta spokesman or to independently confirm the video or the accounts of the fighting.
The Irrawaddy news outlet quoted a fighter from the local People's Defence Force - formed since the coup - as saying the police station had been set on fire and that two civilians had been wounded in the fighting. Reports from other media said up to 15 members of the security forces had been killed.
The Progressive Karenni People Force, a network of local groups, said one fighter had been killed.
Mobye is around 100 km (60 miles) east of the capital Naypyidaw, but lies near territory held by some of the ethnic armed groups that have fought for greater autonomy for decades.
Another clash occurred near the town of Demoso, 20 km (13 miles) south of Mobye, media said. They quoted militia fighters as saying security forces suffered as many as 20 dead and had brought reinforcements with armoured vehicles.
There was no independent confirmation.
A national unity government set up underground by opponents of the coup announced a new flag and command structure for the People's Defence Force, being set up to oppose the army.
An alliance of four ethnic armed groups which are also against the coup battled early on Sunday with security forces in Muse, one of the main crossings to China, Myanmar media said.
While the junta is struggling with new conflicts on several fronts, it also faces daily protests and strikes that have paralysed hospitals, schools and much private business.
More than 125,000 teachers - nearly a third of the total - have been suspended for joining a civil disobedience movement to oppose the coup, an official of the Myanmar Teachers' Federation said.
At least 815 people have been killed by security forces since the coup, according to the Assistance Association for Political Prisoners activist group.
Junta leader Min Aung Hlaing said in comments broadcast on Saturday that 300 people had been killed in addition to 47 police.
Protesters also demand the release of nearly 4,300 people who have been arrested since the coup, including Suu Kyi, 75.
Min Aung Hlaing said Suu Kyi was healthy and would soon appear in court. Her next hearing is on Monday on some of the various charges brought against her.
The army seized power claiming fraud in an election won by Suu Kyi's party in November. Its accusations had been dismissed by the former electoral commission.
In further comments from an interview released by Hong Kong-based Phoenix Television on Sunday, Min Aung Hlaing sought to reassure Chinese businesses after some factories were set ablaze recently in the commercial capital Yangon.
"Our citizens are not being anti-China but it's the politics that cause the hatred," he said.
Some opponents of the coup have accused China of supporting the junta, which has been condemned by Western countries that have introduced limited sanctions. China has been milder in its approach and has said it seeks stability.
The European Union on Sunday denounced a proposal by the election commission appointed by the junta to dissolve Suu Kyi's National League for Democracy.