Four of the slain vigilantes were hunting in the bush near a camp for internally displaced people on the outskirts of the city of Maiduguri when they were seized in a daytime attack.

Vigilante Musa Ari said the attackers were riding motorcyles when they seized six people. Four were later found with their "throats slit".

"Four of our colleagues were killed yesterday (Saturday) by Boko Haram gunmen while they were hunting. Two others are missing and we believe they were taken away by the terrorists," added vigilante Babakura Kolo, speaking from Maiduguri.

In a separate suspected Boko Haram attack on Saturday night, two other vigilantes died after two female suicide bombers detonated explosives in the town of Konduga.

"One of the bombers detonated her explosives close to a group of vigilantes... after they were asked to identify themselves," said vigilante Ibrahim Liman.

"A dusk to dawn curfew has been placed on women in the town following a spate of suicide bombings," he said.

The attacks underline the vulnerability of rural communities in northeast Nigeria at a time when authorities are encouraging people displaced by the Boko Haram conflict to return to their homes and try to rebuild their lives.

On Monday Boko Haram gunmen on motorcycles killed six farmers who were working on their land in Amarwa village near Maiduguri in preparation for the rainy season.

The militant have in recent weeks intensified suicide bombings in and around Maiduguri, the capital of Borno state and birthplace of Boko Haram, with the university campus repeatedly attacked in recent days.

The eight-year Boko Haram conflict has killed 20,000 people and displaced millions from their homes, triggering a food crisis in the ravaged region.

Although Boko Haram has been substantially weakened by the Nigerian military, the group is still capable of launching deadly raids and suicide bombings, putting many people still at risk.