Children were among those killed and injured in airstrikes by Myanmar's military on an ethnic rebel-controlled area in the country's southeast, a humanitarian aid group said Tuesday, as junta forces stepped up their offensive in the region.

Myanmar's military, which seized power in a February 1 coup, has been conducting airstrikes in southeastern Karen state since Saturday night, forcing thousands of residents to flee into the jungles and several neighboring countries, including Thailand and India.

Many of the villages targeted are controlled by the Karen National Union (KNU), an ethnic armed group that holds large swathes of territory in the borderlands.

A 5-year-old boy died in a bombing on Sunday, and a 12-year-old girl was hit in the face by bomb shrapnel, according to relief organization Free Burma Rangers (FBR). The girl had come to Day Bu Noh village to attend school, the group said.