Members of the civilian militia heard that Islamists were planning to attack the town of Benishiek in Borno state, Boko Haram's historic stronghold, said Garba Ngamdu, an aide to the state governor.
The Islamists arrived in the early hours of today morning and a gunfight broke out, Ngamdu added, in accounts corroborated by several vigilante fighters.
"The youths (vigilantes) in Benishiek lost 13 of their members. Twelve died when they were ambushed around 12:30 am (2330 GMT yesterday) and another one died in the hospital," he said.
The governor's aide and wounded vigilante fighters described the clashes to journalists in the Borno state capital Maiduguri, some 70 kilometres from Benishiek.