Pope Francis on Sunday deplored a surge of violence in eastern Democratic Republic of Congo, the victims of which he said included many Christians who had been killed for their faith.

"Painful news continues to arrive of clashes and massacres in the eastern part of the Democratic Republic of Congo," the 87-year-old pontiff said at the end of Sunday Angelus prayer.

"I appeal to the national authorities and international communities to do everything possible to stop the violence and safeguard the lives of civilians."

Francis said "many Christians" were among the victims of the recent bloodshed, "killed in hatred of the faith", describing them as "martyrs".

"Their sacrifice is a seed that germinates and bears fruit and teaches us to bear witness to the Gospel with courage and coherence."

Nearly 150 people have died since the beginning of June in the eastern DRC in killings attributed to Islamic State group-linked rebels.

Congolese authorities blamed the Allied Democratic Forces group for an attack in the Beni region overnight Wednesday which left 42 people dead, including some that had been decapitated.