Myanmar has been in turmoil since Aung San Suu Kyi's civilian government was toppled in a military coup almost two years ago, ending the southeast Asian nation's brief period of democracy.

Four junta fighter jets dropped eight bombs on villages in Hpapun district on Thursday afternoon, killing five people, the Karen National Union said in a statement.

Another four people were wounded, the ethnic rebel group said. The Karen live largely in Myanmar's east near the border with Thailand.

The Myanmar junta was contacted for comment but did not respond.

Christian aid group the Free Burma Rangers said its staff arrived at Lay Wah village in Hpapun hours after bombs destroyed two churches and a school.

"Some villagers had come back and they showed us the mangled bodies of the five who had been killed," the group said in a statement.

"A mother and her baby were instantly killed."

A Baptist pastor and a Catholic priest were among the dead, the Free Burma Rangers statement said. The toddler was almost three.

Villagers had fled into the jungle before the air strikes, the group said, and fatalities would have been much higher had children still been in their classrooms.

"We saw shrapnel-damaged homes and roofs blown off," it said.

A Karen National Liberation Army spokesman told AFP there had been another air strike on Friday.

"We will continue to see these types of incidents because we don't have air defence systems," he said.

More than 2,700 civilians have been killed since the military grabbed power in February 2021, according to a local monitoring group.