Extremist rebels in eastern Congo have killed at least two dozen civilians in separate attacks this week, local authorities and a civil society group said Tuesday.

Rebels with the Allied Democratic Forces, which has ties to the Islamic State group, killed 13 people in Mambasa territory of Ituri province on Tuesday, said Christophe Munyanderu, coordinator for the Convention for the Respect of Human Rights.

Most of the victims were killed in their homes, he said.

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In neighboring North Kivu province, the ADF killed at least 11 people with machetes and guns in Beni territory on Monday, said Col. Charles Ehuta Omeonga, the area's administrator.

Civilians were also targeted in their homes, and the death toll is likely higher because some people are missing, he said.

Violence has been simmering for years in eastern Congo, where about 120 armed groups fight for power, land, minerals or the safety of their communities.

In recent years, ADF attacks have intensified and spread towards Goma, eastern Congo's main city, as well as Ituri province.

Rights groups and the United Nations have accused the ADF of killing hundreds of people and abducting even more, including a significant number of children.