The Ugandan army says it has arrested 70 people across the border, in the northeast of the Democratic Republic of Congo, suspected of hacking to death more than 300 people.
The army maintains a strong presence in the area, in support of a rebel movement opposed to the government in Kinshasa.
An army spokesman, Lieutenant-Colonel Phinehas Katirima, told the BBC the suspected killers were armed bandits known as Ninjas.
He said they had been robbing and murdering people under the pretext that they were witches.