The official, on condition of anonymity, said the militants forced their way into some homes identified to be inhabited by Christians in Musari community near Maiduguri city and slit the throat of 15 people.
Earlier, Lt Col Sagir Musa, a spokesman of the military Joint Task Force deployed by the government to fight terrorism in the area, had given the number of those killed as five.
But a resident confirmed the number of persons killed by the suspected militants as 15.
Boko Haram says it is fighting to install Islamic Sharia rule in Africas top oil producing country.
The country though a secular state, has two major religions; Islam and Christianity.
Christians are found mainly in the south while Muslims are predominant in the north but they share the 150 million population of the country on roughly equal proportion.