U.N. peacekeepers have begun foot and air patrols to protect civilians in Congo's North Kivu province, after a string of grisly attacks left 21 people dead.
The U.N. mission in the DRC, known as MONUSCO, said women, children and an infant were among those killed in the attacks, which took place on Friday and Saturday in the eastern Beni region.
Investigators said the victims included several girls, who appeared to have been raped and beheaded, and a month-old infant.
MONUSCO special representative Martin Kobler said the "atrocities will not go unpunished."
Although there was no initial claim of responsibility for the attacks, provincial officials in North Kivu said they suspect ADF-Nalu, a Ugandan Islamist rebel group.
U.N. forces and Congo's army have been battling the many rebel groups that operate in the mineral-rich eastern DRC.
Last week, one group, the M23, signed a peace agreement with the government.
In November, the group said it was laying down its arms after the Congolese army seized its last stronghold in North Kivu province.
Some information for this report was provided by AP, AFP and Reuters.