Islamic State-backed rebels armed with machetes and hoes have killed at least 52 civilians in the Beni and Lubero areas of eastern Democratic Republic of Congo in recent days, UN and local officials said.

The Allied Democratic Forces (ADF) rebels were taking revenge on civilians after suffering defeats by Congolese forces, Lieutenant Elongo Kyondwa Marc, a regional Congolese army spokesperson, said.

"When they arrived, they first woke the residents, gathered them in one place, tied them up with ropes, and then began to massacre them with machetes and hoes," Macaire Sivikunula, chief of Lubero's Bapere sector, told Reuters over the weekend.

About 30 civilians were killed in the village of Melia alone, Alain Kiwewe, a military administrator for the Lubero territory, told Reuters.

"Among the victims were children and women whose throats were slit in their homes, while several houses were set on fire," he said.

The United Nations Organization Stabilization Mission in the Democratic Republic of the Congo (MONUSCO) condemned "in the strongest possible terms" the attacks by the ADF between August 9 and 16, the mission's spokesperson said on Monday.

The attacks killed at least 52 civilians, including eight women and two children, and the toll could rise as the search is ongoing, the spokesperson said.

The ADF is among several militias wrangling over land and resources in Congo's mineral-rich east.

Congo's army and its ally, Uganda, have intensified operations against the ADF in recent weeks.

In late July, ADF rebels killed 38 people in an attack on a church in eastern Congo.