Relatives and friends of the abducted Nigerian schoolgirls have identified some of them from a video released by Boko Haram Islamist militants.
The footage showed about 130 of more than 200 girls who were kidnapped a month ago from their boarding school in Borno state reciting Koranic verses.
Boko Haram's leader says the captured girls who have not converted to Islam can be swapped for jailed fighters.
Nigeria's government says it is considering all options.
In another development, the country's president is seeking a six-month extension to the year-old state of emergency in three north-eastern states worst hit by Boko Haram attacks.
Meanwhile, the US has revealed it is flying manned surveillance missions over Nigeria to an effort to find the missing schoolgirls.
A team of about 30 US experts - members of the FBI and defence and state departments - is in Nigeria to help with the search. The UK, France and China also have teams on the ground in Nigeria and an Israeli counter-terrorism team is on its way.
The 27-minute footage was shown to some people in Chibok - the town where the girls were kidnapped - on Monday evening.
Not all girls are from Chibok itself as pupils from surrounding areas had come to do their final year exams in April as the school in the town was considered relatively safe.
A community leader in Chibok told the BBC that school friends had identified three of the girls in the video.
A mother had also recognised her daughter from the girls who appear in a group wearing hijabs, the chairman of the parents-teachers association at the school told the Reuters news agency
"The video got parents apprehensive again after watching it but the various steps taken by the governments and the coming of the foreign troops is boosting our spirit, even though I have not seen the any one soldier in Chibok yet," Dumoma Mpur said.
The girls' families have said that most of those seized are Christians, although there are a number of Muslims among them.
Two girls on the video singled out for questioning said they were Christians but had converted to Islam. Another said she was Muslim.
Boko Haram leader Abubakar Shekau said the girls could be exchanged for "our brethren in your prison".
"I swear to almighty Allah, you will not see them again until you release our brothers that you have captured," he said.
Last week, he threatened to sell the girls into slavery.
A Nigerian government statement said "all options" for the girls' release were on the table.
Earlier, Interior Minister Abba Moro appeared to dismiss the militants' offer, saying no exchange would take place. The reason for the discrepancy was unclear.
The BBC's Mark Doyle, in the capital, Abuja, says it appears some sort of negotiations will take place because of the large presence of international advisers in the country, including hostage negotiators.
Boko Haram, whose name 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.
President Goodluck Jonathan - whose government has been heavily criticised for its response to the abduction - said on Sunday that help from abroad had made him optimistic about finding the girls.
He said he believed the girls were still in Nigeria.
The kidnapping has triggered a huge international campaign with world leaders and celebrities calling for the girls to be released.