Insurgents believed to be from the Allied Democratic Forces (ADF) killed residents and burned down houses in the village of Otomabere, Ituri province, according to witnesses.
Congolese army spokesman Jules Ngongo confirmed the ADF attack without giving a death toll, and said Congolese forces were in pursuit of the assailants.
Meanwhile, AFP reports at least 20 people have been killed in a new massacre in DR Congo's eastern province of Ituri, a respected monitor said on Monday, adding that the notorious ADF militia were suspected.
The second attack took place overnight in the village of Bwanasura in Irumu territory, the Kivu Security Tracker (KST) said on Twitter, while volunteers at the local Red Cross said they had counted 36 bodies.
The ADF is a Ugandan militia that moved to eastern Congo in the 1990s.
The group carries out frequent attacks and killed more than 1,300 people between January 2021 and January 2022, according to a United Nations report.
"We were chatting with some friends outside (when) we heard gunshots, and everyone fled in a different direction. It was total panic," said Kimwenza Malembe, a resident of Otomabere.
"This morning we counted 18 dead, killed by knives and firearms," he said.
Irumu chief Jonas Izorabo Lemi said he had received word of 20 dead. Christophe Munyanderu, coordinator of the local group Convention for the Respect of Human Rights (CRDH), also said the provisional death toll was 20.
Further south, in North Kivu province, fighting resumed on Monday between the Congolese army and the M23, a rebel group claiming to represent the interests of ethnic Tutsis, said Congo government spokesman Patrick Muyaya.
The government accuses Rwanda of supporting the M23, which Rwanda denies. The group's resurgence in recent weeks has caused a diplomatic rift between the two neighbors.