Twenty-four vigilantes in northeast Nigeria were killed in an ambush during a botched attempt to arrest members of Islamist sect Boko Haram, one a member of their group and a security source said on Saturday.
"They were ambushed even before they got to the Boko Haram camps," one of the youth vigilantes Masta Moh'd, who was not present during the attack on Friday in the town of Monguno, but had heard from several of the survivors, told Reuters.
He said more than 100 of the vigilantes had participated in the raid, which turned sour when the insurgents, seen as the main security threat to Africa's top energy producer, ambushed them as they entered the town's outskirts.
A member of the government's mixed military and police Joint Task Force, who declined to be named, confirmed the death toll from the incident as 24.
A concerted military crackdown on Boko Haram ordered by President Goodluck Jonathan in mid-May had appeared to have weakened the sect, but they have repeatedly proved masters at going into hiding then coming back just as deadly as before.
The use of civilian militia - often armed with no more than clubs and knives - as a weapon against the Islamists has led to the arrest of hundreds of them, the military says.
That civilian backlash against Boko Haram has handed the military its greatest advantage over the insurgency in the four years it has been active. It has also made the vigilantes and their families prime targets for the Islamists.
Scores have been killed in revenge attacks.
The military said this month that Boko Haram's leader Abubakar Shekau may have died in late July of wounds inflicted during a fire fight with them, although they gave no evidence.
If he is dead, it appears not to have quelled the violence, which is on the rise since the start of the month.