A police official says Boko Haram extremists have killed 18 people at a funeral in northeast Nigeria.

Police spokesman Othman Abubakar said Friday the number of dead could rise.

Witnesses said the assailants shot at mourners after arriving on motorbikes in the Madagali area of Adamawa state on Thursday night.

One witness, who insisted on anonymity citing security concerns, said at least 10 people were injured.

Boko Haram pledged support for the Islamic State group last year. The Nigeria-based group's nearly seven-year-old insurgency has killed some 20,000 people, forced more than 2 million from their homes and spread into neighboring countries.

Recent attacks in southeastern Niger killed more than 20 soldiers and displaced tens of thousands, worsening an already dire humanitarian situation in the region.