Ethnic minority rebels fighting Myanmar's military junta said they had seized a key trading post on the northern frontier, across the border from where China's military was conducting exercises to improve combat readiness and emergency response.
A month of intense fighting between Myanmar's ruling military and an alliance of ethnic minority insurgents has displaced tens of thousands of people in the border region, according to the United Nations, with concern growing in Beijing about instability and an influx of refugees.
The rebellion has presented the biggest battlefield challenge to Myanmar's well-equipped military since it seized power in a coup in 2021.
Emboldened by the northern offensive, pro-democracy militias increase attacks on security forces elsewhere in the country.
The "Three Brotherhood Alliance", as the insurgents call themselves, said they had conquered several towns and the Kyin-San-Kyawt border gate, one of five major trading zones in the township of Muse opposite China.
Late last week, in the same area, a convoy of goods trucks was set ablaze in what the junta called a "terrorist attack". The rebels denied responsibility.
The alliance said it was ready to take its operation to the next level on Monday, having launched coordinated attacks a month earlier to retake territory from the junta and counter the military's air strikes and shelling.
"Via the harmonious operations, the revolutionary forces have seized the junta military's outposts and strategic hills (from which they) were shelling the civilians, by sacrificing their blood, sweat and even lives," it said in a statement.
"We are implementing the objectives of each organisation, and our common objectives, in unity and step-by-step."
Myanmar’s military has vowed to restore order and said it was coordinating with China to maintain stability.
China's forces started combat exercises at the weekend that were due to run until Tuesday, which state media said aimed to "test the rapid manoeuvrability of theatre troops", their combat capabilities and readiness to secure the border with Myanmar.
Myanmar's junta said it was aware of the drills.
The Ta'ang National Liberation Army (TNLA), a member of the rebel alliance, on Monday said it had attacked two military posts in Shan state, with clashes in three locations.
The Kachin News Group on Monday posted video of what it said was thousands of people on motorcycles fleeing the town of Laukkaing in Shan State, fearing an intensification of fighting.
U.N. Office for the Coordination of Humanitarian Affairs last week said 335,000 people had been displaced by the fighting since the coordinated rebel offensive, and were among 2 million forced from their homes since the 2021 coup.
Two videos on social media shared by a minister in Myanmar's anti-junta shadow government showed people gathering on one side of a metal fence covered in razor wire, appealing to Chinese security forces to release a man they said had been detained.
Another video showed displaced people scrambling for cover under a cloud of tear gas on Myanmar's side of the fence.
Reuters could not independently confirm what took place, or when, but was able to verify its location at the Myanmar-China border.