Myanmar resistance fighters on Monday burned the flag used by the military government and raised their own banner at a newly captured army base, as a senior rebel commander vowed they would hold the strategic area near the Thai border.

The celebrations by fighters linked to the armed ethnic Karen National Union (KNU) came less than a week after the capture of Myawaddy, a key trading town on Thailand's western border.

LT Saw Kaw, a soldier of the Karen National Liberation Army (KNLA) in charge of the Cobra column, raises Karen's national flag after burning Myanmar's national flag at a Myanmar military base on the outskirts of Myawaddy.

Myawaddy's fall marked another battlefield loss for the powerful military regime that seized control in 2021 from an elected government led by Nobel laureate Aung San Suu Kyi, who remains in detention.

Simmering anger against the junta has turned into a nationwide armed resistance movement that is now increasingly operating in coordination with established ethnic rebel groups to challenge the military across large parts of Myanmar.

Since last October, the army has lost control of key areas near its borders with both India and China to a loose coalition of allied resistance forces. The loss of Myawaddy at the Thai border could further dent trade revenue for the junta.

In a rare in-person interview, Colonel Nadah Htoo, an operational commander of Brigade 6 of the KNU's military wing that captured the army base, said junta forces have tried and failed to retake the area.

"They have been unsuccessful in making a breakthrough twice now," he said.

He added that the rebels controlled most of the area and would continue to consolidate authority before handing over administration to the KNU's political arm.

"Our military operation will end at the end of April," he said.

A spokesman for the military government did not answer calls on Monday from Reuters.

LT Saw Kaw, a soldier of the Karen National Liberation Army (KNLA) in charge of the Cobra column, burns Myanmar's national flag at a Myanmar military base on the outskirts of Myawaddy.

Faced with the rebel assault, several hundred junta soldiers tasked with defending Myawaddy withdrew from their positions, with a group of less than 200 retreating to near a bridge connecting the Myanmar town with Thailand's Mae Sot.

These soldiers must either surrender to Thai authorities or to the KNU, failing which they may be targeted by resistance troops, Nadah Htoo said.

Thailand's Foreign Minister Parnpree Bahiddha-Nukara said last week that the junta soldiers would be allowed to cross the border if they gave up arms and requested refuge.

Junta leader Min Aung Hlaing said in a speech last month that the forces fighting the military were "destroying the path towards forming a Union based on democratic values and federalism".

But for the allied resistance forces in Myawaddy, Monday was a day to celebrate.

"We are very happy that our revolution has come this far. If we can take more Myanmar bases we will achieve our objective (of overthrowing the junta)," said Myo Myint Keyaw, a 26-year-old fighter in a People's Defence Force, a militia allied with the KNU fighters.

While the rebels celebrated, Reuters reporters in Myawaddy could hear air strikes as fighting raged on the front lines about 40 km (25 miles) to the west, where junta reinforcements were trying to retake the area.

Burnt down houses and buildings riddled with bullets were visible near the captured military base, where stray dogs roamed amongst empty buildings.

On Sunday, a spokesman for the KNU said the rebels had pushed back a second military attempt to break through their lines and advance on Myawaddy.

Myanmar rebels say they have repelled junta push to take back border town

Soldiers from the Karen National Liberation Army (KNLA) prepare to patrol Myawaddy, the Thailand-Myanmar border town under the control of a coalition of rebel forces led by the Karen National Union.

A resistance group fighting Myanmar's military rule said on Sunday its fighters had repelled an attempt by junta troops to advance on the key town of Myawaddy along the Thai border that was seized by the rebels last week.

Reinforcements of junta forces have been trying to advance on Myawaddy for days, but were pushed back in a battle about 40 kilometres away, a spokesperson for the Karen National Union (KNU), Saw Taw Nee, said in an interview.

"It is not easy to come here. They face a lot of difficulty," he told Reuters, saying the KNU's forces had been "blocking and intercepting" the junta troops.

The KNU information could not be independently confirmed. A spokesperson for the military junta that seized power from an elected government a 2021 did not answer calls from Reuters.

The border town of Myawaddy, adjacent to Thailand, was wrested from military control by a coalition of anti-junta forces led by the KNU on Thursday.

Fighting took place on Friday between the villages of Kawkareik and Kaw Nwet along the main Asian Highway 1 leading west from the Thai border, Saw Taw Nee said.

The KNU spokesperson said information received from the front line put the junta's toll of deaths and injuries from the fighting at around 100. "We know that they suffered a loss of one armed carrier and a military truck," he said.

Myanmar has been in turmoil since 2021, when the powerful military deposed an elected civilian government, triggering widespread protests it sought to crush with force.

Simmering anger against the junta turned into a nationwide armed resistance movement that is now increasingly operating in coordination with established ethnic rebel groups to challenge the military across large parts of Myanmar.

Saw Taw Nee said the resistance "will take time". "We need to have a kind of coordination with other groups… to defeat the military," he said.

The KNU spokesperson said there were also challenges working in a broad anti-junta coalition.

"We are still in the process of how to negotiate, how to come together and how to move forward among our Karen groups," he said, referring to members of the ethnic group residing primarily in Kayin State.

Saw Taw Nee said the immediate concern for the KNU is the more than one million displaced people within its territories, and called on the international community, including neighbouring Thailand, to provide support.

"We really need to work together in the future more and more on this issue," he said.

He urged Myanmar's junta to see their recent military setbacks as a sign that they should hand back power to the people.

"Please don’t waste time any more," he said. "This is the time, and a good opportunity, to listen to people first."