Suspected Islamist extremists dressed as soldiers opened fire on residents of a town in northeastern Nigeria on Wednesday after luring them out of their homes, killing four people, residents said.

The incident involving suspected members of Islamist extremist group Boko Haram occurred around 1:00 am in the town of Gamboru Ngala near the border with Cameroon.

Residents said the attack appeared to be in reprisal for the recent arrests of Boko Haram members.

The gunmen dressed in military uniforms went into the Fulatari neighbourhood and called on residents to come out and see Boko Haram members they claimed they had arrested.

"They took up positions and shot whoever came out of his house to see the Boko Haram men they claimed they arrested," Musa Zango, a member of a local vigilante group helping the military hunt Boko Haram members, told AFP.

"They deceived the people in the area into believing they were part of the (vigilante groups) that have sprung up in the town recently to fight Boko Haram."

The gunmen shot dead three residents and strangled another when the gun they fired at him failed, Zango said.

On Monday, troops stationed in the town arrested 17 Boko Haram suspects after a shootout following a tip-off by residents who feared an imminent attack, said Bukar Galadima, a local youth leader.

It was unclear if anyone was killed in Monday's violence.

Wednesday's incident occurred after Nigeria's military on Monday claimed that Boko Haram leader Abubakar Shekau "may have died" from a gunshot wound suffered during a clash with soldiers on June 30.

There has however been no further confirmation and violence attributed to the extremist group has continued.

Boko Haram's insurgency has left at least 3,600 people dead since 2009, including killings by the security forces.

The military launched an offensive in May aiming to end the insurgency and has encouraged the formation of vigilante groups to assist them.

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