GOMA, Congo -- The Congolese army took two more towns in eastern Congo Sunday in fresh fighting against the M23 rebels, said the army spokesman.

The army says it has found two mass graves in Kibumba, a town it took on Saturday, according to the provincial governor.

The army on Sunday gained control of Kiwanja and Buhumba towns in the Rutshuru area of North Kivu province, near Congo's border with Rwanda, army spokesman Lt. Col. Olivier Hamuli told The Associated Press.

The army, using tanks and heavy artillery, is also fighting the M23 rebels in the hills surrounding Kibumba town. The army said it won control of Kibumba on Saturday and now is advancing on the M23 rebels who retreated to the hills toward the Rwandan border.

In Kibumba, the army discovered two mass graves, North Kivu Governor Julien Paluku told AP. The army has been ordered not to touch the graves so that they can be investigated by the government and the United Nations peacekeeping mission to Congo.

United Nations forces are not participating in the fighting, but are in armoured personnel carriers and jeeps with mounted machine-guns several kilometres behind the army forces.