Nigerian security forces say they have killed 20 members of the Boko Haram armed rebel group in the northeast of the country, after the fighters attacked a military base there.
Sunday's attack in the village of Monguno in Borno state followed an unverified video by Abubakar Shekau, the leader of the Boko Haram, was circulated rejecting peace talks with the government and saying attacks will continue.
"Whoever kills any of our member should await a grave retaliation from us," said Shekau in the undated video.
"We will continue waging war against them until we succeeded in establishing an Islamic state in Nigeria."
Sagir Musa, the military spokesman, said that the 20 fighters who stormed the base with gunfire and explosives were killed.
However, he did not say if any soldiers or civilians were killed or wounded in the attack.
Another security official, speaking on condition of anonymity to the AP news agency, confirmed the attack but said details of the incident remained sketchy.
Shekau said that he did not know Sheikh Mohammed Abdulaziz, who proclaimed to be "second-in-command" in Boko Haram and had announced a ceasefire in January, and rejected all his claims and denies any association with the him.
Last week, rebels linked to Boko Haram claimed responsibility for the kidnapping of seven French tourists from northern Cameroon.
Meanwhile, Human rights groups have blamed both Boko Haram and the security forces of violent attacks on civilians in the region.