Gunmen opened fire on a church service in the northeast Nigerian village of Attangara, killing nine people, police and a witness said.
The village is in the Gwoza hills, near the Cameroon border, and the main stronghold of radical Islamist sect Boko Haram, which has killed civilians on an almost daily basis since stepping up its campaign of violence earlier this year.
"As we were holding service, we started hearing gunshots and everybody fled, some through the windows, and ran into the bush," resident Matha Yohana said of Sunday's attack. A police source said nine people were killed in the assault.
"More than 10 of them [the gunmen] were riding motorcycles and one car," she said, adding some local vigilantes had pursued the attackers, killing four of them and detaining three.
Nigeria's military said on Monday that it had arrested a suspect it believed was behind a bomb attack on Sunday that killed 18 people watching soccer on television in the northeast.
There has been no claim of responsibility for the blast that also wounded 19 people in Kabang town in Adamawa state, a stronghold of Boko Haram whose struggle for an Islamic state is centred in the northeast.
Boko Haram is still holding 219 girls abducted from a secondary school on April 14. Nigeria has accepted help from foreign powers such as the United States to try to free them.