Fighters from the Democratic Forces for the Liberation of Rwanda (FDLR) attacked the ethnic Nande civilians in the town of Lubero in North Kivu province at around 2 a.m. (0000 GMT), said Mak Hazukay, a local spokesman for Congo's army.
Hazukay said the killings appeared to be revenge for a series of attacks launched by Nande Mai Mai militias against the FDLR. The Nande, who dominate commerce in North Kivu, are historic rivals of the local Hutu.
"For some time now, the FDLR and Mai Mai have fought over the zone and that has provoked high tensions between the two communities," Hazukay said.
The Centre of Study for the Promotion of Peace, Democracy and Human Rights (CEPADHO), an activist group that documents violence in North Kivu, confirmed the death toll of 14 and said the victims had been shot or hacked to death.
The FDLR's spokesman could not be immediately reached for comment.
Ethnic rivalries, foreign invasions and competition for land and rich mineral deposits among in eastern Congo's dozens of rebel groups have fuelled persistent conflict that has cost millions of lives over the last two decades.
The FDLR, a Hutu militia founded by some of the perpetrators of Rwanda's 1994 genocide who fled into neighbouring Congo, is the largest rebel group, estimated by analysts to have more than 1,000 members.
Congo's army attacked the FDLR last February. The FDLR accuses Congolese forces of collaborating with local rebel groups to attack Hutu civilians, a charge the government denies.
