BANGKOK, Thailand - According to Thailand's official and media sources, fighting has erupted between the Myanmar military and armed ethnic groups near a critical trading corridor near the Thai border.

Witnesses on both the Thai and Myanmar sides of the border reported hearing explosions and heavy machine gun fire near a major bridge from Friday to Saturday.

Last week, fighters from the Karen National Union (KNU), the ethnic armed organization leading the offensive on Myawaddy, seized the last of the Myanmar army's outposts in and around the border town, which is connected to Thailand by two bridges across the Moei River.

The latest clashes began on Saturday morning when Karen groups launched an attack on Myanmar troops hiding near the 2nd Thai-Myanmar Friendship Bridge, a key crossing point for trade with Thailand, according to police commander Pittayakorn Phetcharat in Thailand's Mae Sot district.

He calculated that approximately 1,300 people escaped to Thailand.

Pittayakorn stated that local authorities were searching those who had crossed over for weapons.

"We have given them food and moved them to a safer place," he said.

According to a post on X by Thai broadcaster NBT, the armed groups used 40mm machine guns.

They launched 20 drone bombs on an estimated 200 soldiers who had fled a coordinated assault on Myawaddy and army checkpoints since April 5.

On Saturday morning, a Thai army unit stationed on the border reported that fighting was ongoing, with forces targeting soldiers under the bridge.

"Currently in the middle of fighting, no losses known," the Rajamnu Special Task Force wrote on Facebook.

Thai Prime Minister Srettha Thavisin said he was closely monitoring the situation and that his government was prepared to provide humanitarian help.

"I do not desire to see any such clashes have any impact on the territorial integrity of Thailand, and we are ready to protect our borders and the safety of our people," he posted on X.

Since last October, Myanmar's army has suffered a series of unprecedented defeats, losing vast sections of territory, including border checkposts, to both ethnic militants battling for more autonomy for decades and pro-democracy troops formed following the military takeover.

Myawaddy is essential to the military, as more than $1.1 billion in trade passes through the town yearly.