The Allied Democratic Forces, a militia linked to the Islamic State group, launched raids in several villages in the Mambasa area of Ituri province on Monday morning, they said.
Matadi Muyapandi, a police official in Mambasa district, said 11 corpses had been found "in different parts of the forest."
The army was tracking the rebels in the Irumu area of Ituri, and in the Beni area of the neighboring province of North Kivu, he said.
Mandela Moise, head of a local civil group in the Babila Babombi district of Mambasa, told AFP that 13 people had been killed, most of them farmers.
"ADF rebels ambushed peasant farmers in their fields," Moise said. "Their bodies are still out there."
The Allied Democratic Forces (ADF), historically a Ugandan Muslim majority rebel coalition, established itself in eastern DRC in 1995.
The group is one of the deadliest militias in the strife-torn area. It pledged allegiance to the Islamic State organisation in 2019.
Uganda and the DRC launched a joint military offensive in 2021 to drive the ADF out of their Congolese strongholds but attacks have continued.
Moise said it was a pity the joint army operations were "limited to Irumu and Beni," and the Mambasa district had been "forgotten."
Civil groups said on Sunday they had recorded 23 suspected ADF attacks in January alone in Beni, in which more than 80 people were killed.
In December, the ADF was accused of two attacks in western Uganda in which 13 villagers were killed.
BUNIA, DRC -At least 11 villagers have died in attacks blamed on the ADF rebel group in the eastern Democratic Republic of Congo, local officials said on Tuesday.
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