An ethnic Nande militia in eastern Democratic Republic of Congo killed at least 13 Hutu civilians on Sunday with guns and machetes in an apparent revenge attack for the deaths of Nande civilians last week, a local activist said.

Tit-for-tat massacres by Hutu and Nande militia in eastern Congo's North Kivu province have killed dozens this year. Relations between the communities have worsened due to population movements and operations by the Congolese army against the largest Hutu militia in the area.

Militia violence across the country has spiked in the last week, raising fears that political instability over President Joseph Kabila's tenure could stoke a surge in localized conflicts by creating a local security vacuum.

Mai Mai Mazembe, a predominantly Nande militia, attacked the town of Nyanzale early on Sunday morning, Innocent Gasigwa, spokesman for the Civil Society of Rutshuru territory, said, adding that two militiamen were also killed.

"This must be the response for last time," Gasigwa said, referring to an attack on Thursday by Nyatura, an ethnic Hutu militia, that killed at least 17 civilians in a nearby village.

An army spokesman could not be immediately reached for comment.

At least 40 people died last week in protests against President Joseph Kabila's refusal to step down at the end of his constitutional mandate last Tuesday. The government says he will remain in office until an election can be organized in 2018.

Mediators from the country's Catholic church hope talks between Kabila's ruling coalition and the main opposition bloc will produce a deal by Friday that would see Kabila step down after an election in late 2017.

African and Western powers fear the violence could spark another major conflict in the massive central African nation where millions died between 1996 and 2003 during regional wars and which has never experienced a peaceful transition of power.