The killings took place on Christmas Eve in eastern Kayah state, where pro-democracy rebels have been fighting the military, which took over the government from the democratically elected administration in February.

"In view of the escalating violence in Myanmar, increased international preventive action is required, including an arms embargo," EU foreign policy chief Josep Borrell said.

Myanmar has been in chaos since a military coup in February, with more than 1,300 people killed in a crackdown by security forces, according to a local monitoring group.

Since the coup, the EU has imposed targeted sanctions on the Myanmar military, its leaders and entities.

The bloc also halted EU financial assistance to the government and froze assistance that could be seen as legitimising the military regime.