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.
According to the BBC, 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 their release by Friday, but only two of the girls have been freed, and the circumstances surrounding their release are unclear.
Nigerian presidential spokesman Reuben Abati told the BBC that that the governments of Cameroon and Chad were also involved with the 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.”