Suspected rebels killed at least 30 civilians in the east of the Democratic Republic of Congo on Saturday night, the army says.
The military blamed Allied Democratic Forces (ADF) rebels for the deaths in the village of Rwangoma near the town of Beni in North Kivu province.
The government and the United Nations have blamed the group for repeated violence in the region.
Dozens of protesters gathered in Beni after the Saturday night attack.
Carrying the body of one of those killed, they chanted anti-government slogans, witnesses told AFP news agency.
Army spokesman Mak Hazukay said the attack appeared to be in revenge for military operations in the area.
President Joseph Kabila visited the region last week and said he would work to bring about peace.
The ADF, a Ugandan Islamist group opposed to the Ugandan government, has been in the eastern Democratic Republic of Congo for two decades.
It has been widely blamed for abuses committed against the local population.
There have also been allegations of killings by the military round Beni, but the government has rejected these, placing the responsibility on the rebels.