Boko Haram fighters 'surrender' as alleged chief killed
More than 260 Islamist militants have surrendered in north-eastern Nigeria, the military has said.
Soldiers had also killed a man who featured in Boko Haram's propaganda videos pretending to be the group's leader Abubakar Shekau, it added.
Last year, the military said that Shekau may have been killed, without providing any proof.
Boko Haram has suffered heavy losses in recent weeks in battles in its stronghold of north-eastern Nigeria.
The military said that 135 Boko Haram members surrendered with their weapons in Biu, Borno state, on Tuesday - and that 133 others surrendered elsewhere in north-eastern Nigeria.
The BBC's Will Ross in Lagos says that the claims are impossible to verify.
However, if they are true, it could be a major turning point for the army's campaign against Boko Haram militants, our correspondent adds.
General Chris Olukolade of the Nigerian military said that a man named Mohammed Bashir was among those killed in the latest offensive against Boko Haram last week.
Bashir "had been acting or posing in videos as the deceased Abubakar Shekau, the eccentric character known as leader of the group", he said.
Gen Olukolade did not give further details.
In a statement in August 2013, the military said intelligence reports indicated that Shekau "may have died" in a shoot-out with government forces at a Boko Haram camp in the vast Sambisa Forest, along Nigeria's border with Cameroon, about two months earlier.
But Nigerian journalist Ahmad Salkida, who has good contacts in Boko Haram, says on on his Twitter account that he has it "on authority that Shekau is well and alive".
He said he met Shekau during a failed attempt to negotiate the release of 200 schoolgirls who were abducted by Boko Haram in April.
Who are Boko Haram?
- Founded in 2002
- Initially focused on opposing Western education - Boko Haram means "Western education is forbidden" in the Hausa language
- Launched military operations in 2009 to create an Islamic state
- Thousands killed, mostly in north-eastern Nigeria - but also attacks on police and UN headquarters in capital, Abuja
- Some three million people affected
- Declared terrorist group by US in 2013
Since the abduction, which caused international outrage, a man purporting to be Shekau has appeared in videos, taunting the military and declaring the establishment of a caliphate in areas controlled by Boko Haram.
Speaking at the United Nations Security Council meeting, Nigerian President Goodluck Jonathan urged the council to find more ways to combat the militant threat.
"Evidence has shown that Boko Haram is sourced largely from outside our country," he said.
"Only by united action and firm resolve can we check this urgent threat to humanity and also build the enduring structures that will resist their re-emergence."
"Boko Haram" means "Western education is forbidden" in Arabic, and the group frequently attacks schools and colleges, which it sees as a symbol of Western culture.
The New York-based Human Rights Watch says more than 2,000 civilians have been killed in the region this year.