KINSHASA, Congo (AP) — An extremist rebel group killed at least 12 people in the northeast of Congo, a local civil society organization said Saturday.

The New Congolese Civil Society organization, or NSCC, said the victims were shot dead by the Allied Democratic Forces, or ADF, a shadowy Islamic State group affiliate that has been launching attacks for years from bases in volatile eastern Congo, following a skirmish with a local armed militia.

Conflict in eastern Congo has gone on for decades as myriad armed groups fight for control of valuable mineral resources. There are frequent mass killings, and the violence has triggered an exodus of refugees.

Farmers in nearby villages discovered the bloodied corpses of 12 people in the bush early Friday as they left to work in their fields. John Vuleverio, coordinator of the NSCC, reported that the death toll was still provisional as the search for other bodies continued in the area.

Col. Jean-Baptiste Munyampazi, the administrator of the territory where the bodies were found, declined to provide an official death toll, indicating that government soldiers stationed in the area were actively tracking down the alleged perpetrators.

In June, the ADF is suspected to have killed at least 41 people — most of them students — in a brutal attack on a school in Uganda, near the border with Congo.