The military sent troops backed by air support to an insurgent camp to carry out the raid, military spokesman Sagir Musa told reporters in the city of Maiduguri on Friday.

"Troops pursued the terrorists to their camps with air support and about 50 insurgents were killed in a shootout," Musa said. "Troops are pursuing the remnants of the fleeing terrorists by blocking all possible escape routes."

The military had ordered the raids after gunmen suspected to be from Boko Haram killed 15 people at a market in the town of Gajiram on Wednesday. Gunmen suspected to be from the militant group were also responsible for an attack in Bulaulin-Ngabura village on Thursday, which killed nine people.

The latest violence occurred in Borno state, the historic Boko Haram stronghold where the military has been in conflict with insurgents for four years. Most of the region has been under a state of emergency since May, when the military launched a campaign to curb violence stemming from the group.

The militants have been targeting vigilante groups formed to defend the local population. Some civilians have been supportive of the vigilantes, including Nigeria's Chief of Army Staff Azubuike Ihejirika, who called them "youth volunteers" who have "greatly supported the Nigerian army."

However, others have voiced concern that they would exacerbate the conflict and potentially commit human rights abuses.

More than 1,700 people have been killed in Boko Haram attacks since 2010. Violence has increased in recent weeks after an initial decline that coincided with the military's campaign.

dr/lw (AP, AFP)