Nigeria says it is still holding talks with Boko Haram, two weeks after the government said it had agreed a truce with the Islamist militant group.
A presidential spokesman said he was optimistic that something "concrete and positive" would come out of the talks.
There has been no comment from Boko Haram, and violence in northern Nigeria has continued.
More than 200 schoolgirls are still being held by the group, which has been fighting an insurgency since 2009.
The military had said they were expecting the schoolgirls' release by 24 October.
At least 2,000 civilians have been killed by Boko Haram this year.
The group has taken more than 500 women and girls hostage since it began its insurgency in 2009, according to Human Rights Watch.
At least one girl who was abducted by Boko Haram about a week ago has been freed, reports the BBC's Abdullahi Kaura Abubakar from Nigeria.
The circumstances surrounding her release are unclear.
Contrary to an earlier report, she was not among the more than 200 schoolgirls who had been abducted in April from their boarding school in Chibok, Borno state.
That abduction sparked global outrage, and the schoolgirls' continued captivity has led to criticism of the Nigerian government's efforts to secure their release.
Nigerian presidential spokesman Reuben Abati told the BBC that the governments of Cameroon and Chad were involved with the latest negotiations.
Their involvement is viewed as significant because Boko Haram frequently move across borders.
Mr Abati added that it was "difficult to put a time frame" to the negotiations.
Nigerian presidential aide Hassan Tukur had previously told the BBC's Focus on Africa programme that the arrangements for release of the schoolgirls would be finalised at a meeting this week in Chad's capital, Ndjamena.
Many Nigerians do not believe the government's claims of a ceasefire with Boko Haram.
Mr Abati responded to criticism of the military by saying: "We must realise that what the Nigerian military is facing is an unusual situation."
"I think that what the Nigerian military deserves and requires at all times is encouragement."
In May 2013, President Goodluck Jonathan imposed a state of emergency in the northern states of Borno, Yobe and Adamawa, vowing to crush the Islamist insurgency.
But Boko Haram increased its attacks this year.
The group promotes a version of Islam which makes it "haram", or forbidden, for Muslims to take part in any political or social activity associated with Western society.
It frequently attacks schools and colleges, which it sees as a symbol of Western culture.