Nigeria's new president has said he is willing to negotiate with Boko Haram leaders for the release of more than 200 schoolgirls kidnapped last year.
Muhammadu Buhari told CNN it would depend on the credibility of those saying they represented the Islamist militant group.
"Our main objective as a government is to secure these girls safe and safe," he said during a visit to the US.
A previous prisoner-swap attempt for the girls' release ended in failure.
The kidnap of the girls from a boarding school in the north-eastern town of Chibok in April 2014 sparked global outrage.
The mass abduction sparked one of the biggest social media campaigns last year, with the Twitter #BringBackOurGirls being used more than five million times.
Boko Haram, thought to be responsible for more than 10,000 deaths since 2009, has stepped up attacks since Mr Buhari took office in May, vowing to tackle the insurgency "head on".
'Arms dealer arrested'
"If we are convinced that the [Boko Haram] leadership that presented itself can deliver these girls safe and sound, we'll be prepared to negotiate what they want," President Buhari, a former Nigerian military ruler, told the US broadcaster.
"We have to be very careful about the credibility.... [of those] claiming that they can deliver... we are taking our time because we want to bring them safe back to their parents".
He told CNN that bringing security to stabilise Nigeria - both in dealing with the oil militants in the south as well as the Islamist insurgents in the north-east - was his main priority.
"Nothing will work until this country is secure," he said.
In last seven weeks, he has replaced his military chiefs, moved the military headquarters to the north-east and organised for the deployment of a multi-national force to fight Boko Haram by the end of July.
Meanwhile, a Nigerian spokesman has told the BBC that the multi-national force has arrested a suspected arms dealer in Chad who was allegedly supplying weapons to the militants.
Mr Buhari was speaking in Washington after meeting US President Barack Obama and World Bank officials about securing help to tackle Boko Haram.
The US has committed $5 million (£3.2m) to the fight against the insurgents since his election.
And the World Bank has pledged $2.1bn to help rebuild north-eastern parts devastated by the insurgency, Mr Buhari said on Tuesday.
Many villages and towns have been burnt down during six-year insurgency and more than one million people have fled their homes.
The Chibok schoolgirls have not been seen since last May when Boko Haram released a video of around 130 of them gathered together reciting the Koran.
Some of those who were kidnapped have been forced to join the militant group, the BBC was told last month.
Amnesty International estimates that at least 2,000 women and girls have been abducted by Boko Haram since the start of 2014.
Boko Haram at a glance
- Founded in 2002, initially focused on opposing Western-style education - Boko Haram means "Western education is forbidden" in the Hausa language
- Launched military operations in 2009
- Joined Islamic State, now calls itself "West African province"
- Thousands killed, mostly in north-eastern Nigeria, abducted hundreds, including at least 200 schoolgirls
- Seized large area in north-east, where it declared caliphate
- Regional force has retaken most territory this year
- But suicide attacks have increased May 2015