Suspected Boko Haram gunmen kidnapped eight girls aged 12 to 15 from a village near one of their strongholds in northeast Nigeria.

"They were many, and all of them carried guns. They started shooting in our village," said Lazarus Musa, a resident of Warabe.

A police source 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 April 14.

The United Nations warned Islamist Boko Haram militants yesterday that there was no statute of limitations if they carried out their leader's threat to sell the schoolgirls kidnapped last month.

Boko Haram leader Abubakar Shekau said in a video released on Monday that Allah had told him to sell the girls taken by his fighters on April 14.

"We warn the perpetrators that there is an absolute prohibition against slavery and sexual slavery in international law. These can constitute crimes against humanity," UN human rights spokesman Rupert Colville said. "That means anyone responsible can be arrested, charged, prosecuted and jailed at any time. So just because they think they are safe now, they won't necessarily be in two, five or 10 years' time," he said.