Suspected Boko Haram gunmen kidnapped eight girls aged between 12 and 15 from a village near one of their strongholds in north-east Nigeria on Monday night, police and residents said on Tuesday.
"They were many, and all of them carried guns. They came in two vehicles painted in army colour. They started shooting in our village," said Lazarus Musa, a resident of Warabe, where the attack happened.
A police source, who could not be named, said the girls were taken away on trucks, along with looted livestock and food.
The Islamist rebels are still holding more than 200 girls they abducted from a secondary school on 14 April.
Their plight and the failure of the Nigerian military to find them has drawn international attention to an escalating Islamic extremist insurrection that has killed more than 1,500 so far this year.
Boko Haram, which translates as "western education is sinful", has claimed responsibility for the mass kidnapping and in a video released on Monday the group's leader, Abubakar Shekau, said Allah had told him to sell the girls.
The United Nations warned Islamist Boko Haram that there was no statute of limitations if they carried out their leader's threat.
"We warn the perpetrators that there is an absolute prohibition against slavery and sexual slavery in international law. These can under certain circumstances constitute crimes against humanity," UN human rights spokesman Rupert Colville told a news briefing in Geneva.
"That means anyone responsible can be arrested, charged, prosecuted, and jailed at any time in the future. So just because they think they are safe now, they won't necessarily be in two years, five years or 10 years' time," he said.
He also urged Nigeria's federal and local authorities to work together to rescue the girls.