Updated

Nigerian police say they are investigating the deaths of eight herdsmen allegedly killed early this month by vigilantes hunting Islamic militants near the Niger border.

Borno state Commissioner of Police Lawan Tanko said the attack took place on Nov. 5 but was not reported to police for nearly two weeks because the state is virtually without mobile phone service for security reasons.

Borno and two other northeastern states have been under emergency rule for over six months as the government battles Boko Haram, a militant group that has killed thousands of people in the past four years.

Civilian vigilante groups sanctioned by security forces have risen up in all three states against Boko Haram. Residents say they fear the attack on the herdsmen will spark further violence.