Nigeria’s military has killed a top commander of militant Islamist group Boko Haram in the north-eastern city of Maiduguri, an army spokesman has said.
Ibn Saleh Ibrahim was killed in an exchange of fire with six of his lieutenants, the spokesman added.
An unknown number of civilians are said to have been killed in the crossfire, says a BBC reporter in Nigeria.
Boko Haram, which has killed hundreds of people since 2009, has not commented on Mr Ibrahim’s reported death.
The group’s founding leader, Mohammed Yusuf, was killed by security forces in July 2009.
Boko Haram is now said to be led by Abubakar Shekau.
Army spokesman Lt Col Sagir Musa told the BBC that Mr Ibrahim was “very close” to Mr Shekau and had a reputation of being “invincible”.
“Yesterday [Thursday], we learned he was in town and we were able to track him in a special operation,” he said.
“There was an exchange of fire and in the process he was killed with six of his lieutenants.”
There has been no independent confirmation of Mr Ibrahim’s role in Boko Haram.
Lt Col Musa said Mr Ibrahim had been responsible for last month’s assassination of retired General Mohammed Shuwa following an order from Mr Shekau.
Gen Shuwa was shot dead at his home in Maiduguri – no group has said it carried out the attack.
He is regarded by the Nigerian military as a war hero, and played a key role in crushing Biafran separatists during Nigeria’s brutal civil war in the 1960s.
In a statement, Lt Col Musa said the operation in Maiduguri, supported by armoured personnel carriers and helicopters, was on-going.
Weapons and explosive devices have been recovered, he added.
The BBC’s Abdullahi Kaura in the northern city of Kaduna says residents in Maiduguri told him that the security forces have sealed off four areas within the city – Ngarnam, Bulabulin, Bayan Quarters and Flatari.
This has made it impossible for people to move in and out of the areas, though some managed to flee on Thursday when fighting broke out, he adds.
Military helicopters were circling the suspected Boko Haram strongholds, but no shooting was heard on Friday, our reporter quotes residents as saying.
Residents also told our reporter that during Thursday’s clashes, civilians, including women and children, were killed after being caught in the crossfire.
The number of casualties is not known.
Earlier this month, rights group Amnesty International accused Nigeria’s security forces of carrying out widespread abuses in their campaign against Boko Haram, including extrajudicial killings, enforced disappearances and torture.
The group is campaigning to impose Islamic law across Nigeria.
It has carried out a wave of bombings and assassinations since 2009.