Several Thai army vehicles, equipped with roof-mounted machine guns, patrolled the streets of Mae Sot, even as the sound of explosions and heavy fighting rang out from across the border in Myawaddy, four local residents said.
"Security in the town is tighter than before. My neighbour was checked by Thai soldiers when she went near the border area," a Myanmar citizen sheltering in Mae Sot said, declining to be named.
"The soldiers are patrolling along the border, checking everyone."
Two Thai military commanders told local media that fighting was ongoing around Myawaddy, a strategically vital trading outpost that was attacked by the Karen National Union (KNU) and allied anti-junta groups.
In a statement last week, the KNU said its troops had attacked a junta camp near Myawaddy, forcing some 600 security personnel and their families to surrender.
A junta spokesman did not respond to a call from Reuters seeking comment.
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.
Junta troops have already lost control of swathes of territory along Myanmar's borders with Bangladesh, China and India, with the military now facing its biggest test since first taking control of the former British colony in 1962.
The well-armed military has also depleted most of its battalions to below their recommended troop level following months of relentless fighting, and is now pushing a conscription law to recruit more soldiers.
