In the video, released by Boko Haram, its leader says the girls will be freed only if imprisoned militants are released
Nigeria has insisted it will not agree to a request to free imprisoned Islamic militants in return for the release of dozens of kidnapped schoolgirls.
Interior Minister Abba Moro said Boko Haram, the group holding the girls, was in no moral position to make the offer.
However, the information ministry had earlier said all options were on the table, after the group released a video of the girls and suggested a swap.
Boko Haram snatched more than 200 girls from a school on 14 April.
About 50 children escaped, and it is not known how many are still being held.
The video released on Monday showed 136 girls, and was interspersed with militants explaining that they had “converted” to Islam.
Three of the girls – wearing full-length cloaks – are shown speaking. Two say they were Christian and have converted, while the other says she is Muslim.
The US state department said intelligence experts were closely examining the footage for clues to the girls’ whereabouts.
Boko Haram leader Abubakar Shekau said on the video: “For those who have not accepted Islam, I swear to Allah we will never release them until after you release our brethren in your prison.”
A man who is related to three of the girls said the video at first gave him hope, but then made him anxious and tearful.
“Maybe they are converted into another religion by force, so it truly is a kind of terrifying situation,” said the man, who did not want to be named.
Earlier reports said some of the girls had been married off to their captors, and Abubakar Shekau had also threatened to sell some of them.
Nigerian Interior Minister Abba Moro says a prisoner swap is “not on the table”
After the video was released, an information ministry statement said the government would “continue to explore all options for the release and safe return of our girls”.
However, Mr Moro later told the BBC that the government would not agree to any kind of exchange.
“As far as this government is concerned, the option of [the] swap of innocent citizens with people who have taken arms against the country… is not on the table,” he said.
The BBC’s John Simpson: “This whole part of Nigeria is Boko Haram territory”
Boko Haram, which means “Western education is forbidden”, had previously said the girls should not have been at school and should get married instead.
The militants have been engaged in a violent campaign against the Nigerian government since 2009.
Nigerians have joined together to pray for the girls
The children’s plight has sparked a global campaign
The video shows 136 girls, three of whom speak to the camera
The government has faced heavy criticism of its response to the mass abduction.
President Goodluck Jonathan said on Sunday that assistance from abroad had made him optimistic of finding the girls.
The UK and US already have teams helping on the ground in Nigeria and an Israeli counter-terrorism team is also on its way to the country. (BBC)