Suspected members of Nigeria's Islamist group Boko Haram shot dead more than 20 civilians when a vigilante group attacked them in the northern Borno state, a military spokesman said Sunday.

"The suspected sect members came armed and fired sporadic shots that killed over twenty innocent civilians," Haruna Mohammed Sani, spokesman for the Multinational Joint Task Force (MNJTF) said.

The violence took place on Saturday in Dawashe village, the army lieutenant said in a statement.

He said men from the Civilian Joint Task Force, a vigilante group formed in Boko Haram's bastion Maiduguri to combat the Islamist gunmen who have been terrorising the region for years, entered Dawashe to search for suspects.

Suspected Boko Haram members subsequently opened fire in the village, the spokesman said, adding that the victims were mostly fishermen and traders.

Sani said a dozen other civilians sustained gunshot wounds during the incident but provided no information on casualties among the belligerents.

The toll and circumstances of the incident could not immediately be verified independently.

The MNJTF, a joint military force set up in 1998 to combat border crimes, consists of troops from Nigeria, Chad and Niger.

Its mandate was recently expanded to fight Boko Haram, whose insurgency is estimated to have cost 3,600 lives since 2009, including killings by security forces.

The Cilivian JTF emerged in May after the state of emergency was declared in the region.

It consists of local youths who are generally armed with bows and arrows, machetes, cudgels, and axes but no guns.

The MNJTF has recognised them as an organisation, giving them training and ID cards, and effectively using them as a proxy militia.

The group's knowledge of the terrain and local languages also means it has become a valuable intelligence gathering asset for the government.

Suspected Boko Harm members late Friday attacked youth vigilantes operating in Mainok town, Borno state, killing one of them and injuring another, a military spokesman said.

JTF troops have been deployed to Mainok and surrounding villages in a bid to arrest the attackers, he said, without giving further details.