Some 200 Myanmar military personnel withdrew to a bridge connecting the border town of Myawaddy to Thailand on Thursday following a days-long assault in the area by anti-junta rebels, according to an ethnic armed group spokesman and local media.
Myanmar's military-run government is battling armed rebel groups on several fronts and has suffered a string of defeats in frontier areas.
The retreat of junta troops in Myawaddy, which is adjacent to Thailand's Mae Sot, signals the potential loss of another key border trading outpost that has direct highway access to parts of central Myanmar.
On Thursday, around 200 fleeing soldiers were gathered at a border crossing into Thailand, said Saw Taw Nee, spokesperson for the Karen National Union (KNU), an anti-junta group leading the assault on Myawaddy.
Local news outlet Khit Thit reported Thai authorities were in talks with the soldiers to decide whether to grant them refuge.
A spokesperson for the Myanmar junta did not respond to calls for comment.
The KNU said last week that its troops had attacked a junta camp near Myawaddy, forcing some 600 security personnel and their families to surrender.
Border crossings in the area were open for civilians who have been coming into Thailand from Myanmar in large numbers, said Police Colonel Borwornphop Soontornlekha, superintendent of immigration in the Thai province of Tak, where Mae Sot is located.
"Usually there are about 2,000 people who cross into Mae Sot from Myawaddy each day, but the last three days the number was almost 4,000 per day," Borwornphop told Reuters.
Thailand's military has stepped up security on its side of the border, deploying army vehicles equipped with roof-mounted machine guns.
At least 2,000 people have been displaced within Myanmar by the latest round of fighting between the rebels and the military, according to civil society group Karen Peace Support Network.
Myanmar's military, which took power in a 2021 coup after deposing an elected civilian government, has faced a series of setbacks against a loose alliance of ethnic rebel groups and a civilian militia movement.