More than 20 people, including women and children, have been killed in eastern Democratic Republic of Congo, UN peacekeepers say.
Most appeared to have been hacked to death on Friday and Saturday in two villages in North Kivu, including three girls who were raped and then beheaded.
It is not clear who carried out the attacks, but the UN mission said the atrocities would "not go unpunished".
The attacks took place near the town of Beni, which is about 250km (150 miles) north of Goma.
The youngest victim is thought to have been only a few months old," the UN Organization Stabilization Mission in the Democratic Republic of the Congo (Monusco) said.
Three girls appear to have been raped and then beheaded. A child's dismembered body is said to have been found in a tree, in the village of Musuku, the statement said.
Officials and civil society organisations in North Kivu accused the Allied Democratic Forces-National Army Liberation of Uganda (ADF-Nalu) of carrying out the attacks.
The ADF-Nalu is considered to be the only Islamist organisation in the region.
The UN has more than 19,000 troops in DR Congo, with an attack force given the mandate of neutralising armed groups.
Analysts say the killings highlight the challenges faced by UN and Congolese forces in eastern Congo, despite the defeat of the M23 rebels.
The government signed a peace deal last week with the rebel movement, which took up arms in April 2012, accusing the authorities of marginalising the ethnic Tutsi minority and failing to honour previous peace accords.
Eastern DR Congo has been wracked by conflict since 1994, when Hutu militias fled across the border from Rwanda after carrying out a genocide against Tutsis and moderate Hutus.