A new video issued by Islamist militants, Boko Haram claims to show some of the nearly 300 schoolgirls missing in Nigeria, who the group's leader says have converted to Islam.AFP reported that Boko Haram's leader said the girls would not be released until members of the terror group being held in prison are freed.
Police say a total of 276 girls were abducted on April 14 from the northeastern town of Chibok, in Borno state, which has a sizeable Christian community. Some 223 are still missing.
In the video, Abubakar Shekau speaks for 17 minutes before showing what he says are about 130 of the girls, wearing full-length hijabs and praying in an undisclosed rural location.
One of the girls then appears to talk directly to the camera.
None of the youngsters appears to be visibly distressed, but it appears as if they are clearly under duress.
Holding a pad of paper in his hand, Mr Shekau tells the camera: "These girls, these girls you occupy yourselves with their affair we have indeed 'liberated' them.
"Do you know 'we have liberated them'? These girls have become Muslims. They are Muslims."
He continues: "It is now four years or five years that you arrested our brethren and they are still in your prison.
"You are doing many things (to them). And now you are talking about these girls. We will never release them until after you release our brethren."
Sky's Special Correspondent Alex Crawford who has spoken to a father of one of the kidnapped girls says he does not want the government to release Boko Haram prisoners in exchange for his daughter.
He told her: "Its not right. They'll do it again."
A special adviser to the country's president Doctor Reuben Abati told Alex Crawford there were lines the government would not cross in the hunt for the girls.
Speaking after it was revealed authorities had made indirect contact with Boko Haram, Dr Abati said: "The government of Nigeria has no intention to pay a ransom or to buy the girls, because the sale of human beings is a crime against humanity.
"The determination of the government is to get the girls and to ensure that the impunity that has brought this about is checked and punished."
Boko Haram's leader Abubakar Shekau has threatened to sell the girls "at the market" and some are believed to have already been taken out of the country.
The search for the girls remains centred on the huge Sambisa forest, which is three times the size of Wales.
Intelligence sources have told Sky News that Nigeria's neighbours - Chad, Cameroon and Niger - are providing help to find the teenagers.
Sky News sources have also learned the militants are likely to have laid booby traps and landmines to stop the girls being found.
Israel has become the latest country to offer to help the search effort. Experts from Britain, France and the US are already in the country.
France has called for African leaders to hold a summit focused on the issue.