Gunshots and explosions have been heard near the northeastern Nigerian city of Maiduguri.
Security forces are reportedly battling a large number of fighters suspected to be members of the Boko Haram armed group.
"According to our sources in Maiduguri, gunmen ... sneaked under the cover of darkness this evening and tried to infiltrate Maiduguri," Al Jazeera's Ahmed Idris, reporting from Sierra Leone's capital, Freetown, said on Sunday.
"They attacked two villages on the outskirts of Maiduguri. There are reported casualties and several people have been wounded," he added.
"The army so far was able to repel the attackers. Our sources are telling us that at least 10 bombs went off and there was some gunfire."
Maiduguri, the capital of Borno state, has been frequently targeted by Boko Haram since the group launched its armed campaign nearly a decade ago.
On Friday, four female suicide bombers in their teens detonated their explosives near the city, killing one more person, according to police.
The Boko Haram armed campaign has claimed more than 20,000 lives and forced some 2.7 million people to flee their homes.
