Residents of a northern Nigerian village say suspected Boko Haram militants have kidnapped eight more girls in the region.
The residents of Warabe said Tuesday that gunmen stormed their village Sunday and kidnapped the girls. They say the kidnappers, who were in several vehicles, also took food and livestock during the raid.
Their allegation follows Boko Haram's claim of responsibility for abducting more than 300 school girls in mid-April from Chibok, another town in Borno state. Some of the girls managed to escape but 276 remain missing.
In a video released Monday, Boko Haram leader Abubaker Shekau said "I abducted your girls," and vowed to sell them in the market.
In another development, the United Nations human rights office has warned Islamist militants they could face charges of crimes against humanity if they carried out the threat to sell the kidnapped girls.
In a Tuesday briefing, a spokesman for U.N. rights chief Navi Pillay said under international law, it would be "one of the most serious crimes" that exists. The spokesman also said those responsible for such a crime could be arrested, prosecuted and "jailed at any time in the future."
Also Tuesday, Britain said it was supporting the Nigerian government's efforts to find the girls.
British Foreign Secretary William Hague said his government is offering "practical help" to Nigeria.
"What has happened here with the actions of Boko Haram in using girls as the spoils of war, the spoils of terrorism is disgusting, it is immoral, it should show everybody across the world that they should not give any support to such a vile organization."
The U.S. said Monday that it is giving Nigeria counterterrorism assistance.
White House spokesman Jay Carney called the abductions a "terrible tragedy" and said U.S. national security officials are closely monitoring the situation.
"Our counterterrorism assistance to Nigeria focuses on information-sharing, on improving Nigeria's forensics and investigative capacity. It also stresses the importance of protecting civilians and ensuring that human rights are protected and respected. We are working with the Nigerian government to strengthen its criminal justice system and increase confidence in the government by supporting its efforts to hold those responsible for violence accountable."
Some Nigerians have been critical of the government, saying President Goodluck Jonathan's administration has not done enough to secure the girls' release. But in a VOA interview , ruling People's Democratic Party spokesman Abdullahi Jalo said Mr. Jonathan is doing everything possible.
"He reaffirmed to people that no matter what, the government will spend its last blood, its last effort to see that these people, these girls, are returned to their loved ones."
During a televised appearance on Sunday, President Jonathan said he had ordered his top security officials to do all they could to secure the girls' release.
Unconfirmed reports say some of the girls have been "married" to their captors, while others allegedly have been moved across the border into Cameroon and Chad.