Nigerian militants 'kill 15 and slit throats'
In a second attack, gunmen killed two people, including a policeman, and burnt down government buildings in Maiha, on the border with Cameroon.
No group has claimed responsibility.
In Musari, near Maiduguri, a school teacher told the Associated Press news agency that gunmen had gathered people into a group before massacring them.
The teacher said 15 people had died in the attack; many had had their throats slit.
An unnamed relief worker told Agence France-Presse: "From the information we gathered, the attackers broke into selected homes and slaughtered 15 people in their sleep."
"The victims were selected because they were all Christians, some of whom had moved into the neighbourhood from other parts of the city hit by Boko Haram attacks," the relief worker added.
The Nigerian military said it had arrested three people and seized weapons following the attack outside Maiduguri.
A military spokesman said just five people had been killed. Security officials routinely understate casualty figures in Nigeria.
In the attack in Maiha, also on Friday, suspected militants released 35 prisoners from a local prison before setting it on fire, prison and police officials said.
Violence linked to the Boko Haram insurgency - a group seeking to impose Islamic law on the country - has claimed hundreds of lives in 2012.
Six people died in an attack on a church on Christmas Day, while seven people were killed on Wednesday in Maiduguri, the city where Boko Haram launched its campaign in 2009.
Nigeria is divided between a mainly Muslim north and a Christian south.