The attack occurred late last night in the Madagali area of Adamawa state near the Sambisa forest, which has long been a stronghold for the Nigeria-based Islamic extremist group.
"They stormed our village on motorbikes and immediately opened fire on the people observing the wake," said a witness who insisted on anonymity, citing security concerns.
The witness said at least 10 injured people were rushed to a health facility in the nearby town of Gulak.
Police spokesman Othman Abubakar confirmed early reports that 18 people were killed and warned the toll could rise.
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"There was pandemonium during which many people scampered for their lives," Kamale said.
Boko Haram pledged support for the Islamic State group last year. The 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.