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.

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.

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, 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.