At least 15 people were killed by extremist attacks in eastern Congo's North Kivu province, a rights group said Friday.

Fighters with the Allied Democratic Forces —believed to have ties with the Islamic State group — attacked people for multiple days this week in the Ruwenzori sector of Beni territory, said Meleki Mulala, a coordinator for the New Congolese Civil Society group, a local rights organization.

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“They (also) seriously injured several other civilians who were dispatched for urgent care," he said. The attackers executed the victims with knives, and the bodies of the dead were taken to the morgue and will be buried, Mulala said.

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Violence has simmered for decades in eastern Congo, where about 120 armed groups fight over land, resources and power, and some to defend their communities.

Attacks by the Allied Democratic Forces have increased recently.

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This week's violence comes days after at least 18 people were killed by the group in neighboring Ituri province and weeks after 17 people were killed, also in North Kivu.