YANGON: At least 2,500 people including hundreds of children have fled a flare-up in fighting between the Myanmar army and ethnic minority rebels and have taken refuge across the border in Thailand, Thai authorities and an aid group said.

Those displaced had poured into the Thai town of Mae Sot after fighting in the past few days between the Karen National Union (KNU) and Myanmar's army, Somchai Kitcharoenrungroj, deputy governor of western Tak province, told a news conference.

Myanmar was plunged into turmoil when the military ousted a civilian government led by Nobel laureate Aung San Suu Kyi on Feb. 1, triggering protests in cities and sporadic clashes in the countryside between anti-junta militia and the army.

There has also been intensified fighting at times between the army and ethnic minority insurgents in border areas, like the KNU, Myanmar's oldest rebel force.

Somchai put the number of displaced on the Thai side of the border at 2,503. Ye Min, an official at the Aid Alliance Committee, a Thai-based Myanmar migrants group, said that total included 545 children.

"We are providing food assistance working together with Thai authorities," Ye Min said by telephone, adding most of the displaced were from Lay Kay Kaw and other villages.

The KNU has been seeking self-determination in a region of about 1.6 million people.

The KNU said in a social media post said four Myanmar soldiers were killed and four wounded during the fighting on Wednesday.

A report by Public Voice Television, which is backed by Myanmar's shadow government, posted photographs it said showed seized weapons and eight captured members of the Myanmar security forces.

It said 18 government soldiers had been killed.

Reuters could not independently verify the claims and a spokesman for Myanmar's military junta did not answer a call seeking comment.

Tak provincial authorities said there was a clash between the army and the KNU on Thursday about 500 metres (550 yards) from the Thai border.

It said a shell had fallen on the Thai side of the border though had not caused harm or damage, and Thai forces had intensified patrols in the area.