Five people were hacked to death on Wednesday in Maiduguri in northeastern Nigeria, police said, the latest attack in the stronghold of Islamist sect Boko Haram.
Separately, residents and a Reuters witness said they heard a loud explosion and around 30 minutes of gunfire in the town, close to borders with Niger and Chad.
Boko Haram killed hundreds of people last year in an attempt to carve out an Islamic state in a country of 160 million split roughly equally between Christians and Muslims.
The group is the biggest security threat to Africa's leading oil producer and its insurgency has fed a general rise in criminality in Nigeria's mostly Muslim north.
Two witnesses, who asked not to be named, said they heard cries for help at around 2:30 a.m. from a house in the Jiddari Polo area of Maiduguri and later saw five dead bodies with what looked like machete wounds.
"Five people were slaughtered today but we can't say who did it because they fled before security personnel arrived," police spokesman Gabriel Jibrin said by phone.
Military and police said it was too early to give any details on any casualties from the explosion and gun battle.
Gunmen suspected of being members of Boko Haram killed 13 local hunters who sell bush meat Islamist militants disapprove of in Maiduguri on Monday.
Nigeria plans to deploy around 1,200 troops as part of a West African intervention force to combat Islamist militants occupying the north of Mali, and officials fear Nigeria's involvement could further inflame its own insurgency.
President Goodluck Jonathan said on Tuesday that tackling global jihadists was in Nigeria's interest because of the links between its Islamists and those in the desert states to the north, such as Mali.
An Islamist group known as Ansaru, which has been blamed for abducting and killing Westerners, claimed responsibility for an attack on Nigerian troops heading to Mali on Sunday that killed two officers.
Gunmen fired on the convoy of one of Nigeria's most senior Islamic leaders in Kano on Saturday, killing at least four people.
(Reporting by Ibrahim Mshelizza and Isaac Abrak; Writing by Joe Brock; Editing by Alison Williams)