Boko Haram kidnapped more than 250 girls from a secondary school in Chibok in remote northeastern Nigeria on April 14 and has threatened to sell them into slavery, while eight girls were taken from another village earlier this week.

"The members of the Security Council expressed their intention to actively follow the situation of the abducted girls and to consider appropriate measures against Boko Haram," said a statement by the 15-member council, which includes Nigeria.

The Security Council statement "demanded the immediate and unconditional release of all abducted girls still in captivity and further expressed their deep concern at statements made by the alleged leader of Boko Haram threatening to sell these girls as slaves."

Several countries, including the United States, Britain, France and China, have offered support to Nigeria to help find the girls. British experts including diplomats, aid workers and Ministry of Defense officials arrived in Nigeria on Friday to advise the government on the search.

UN Secretary-General Ban Ki-moon said on Thursday that Nigerian President Goodluck Jonathan had accepted his offer to send a high-level UN envoy "to discuss how the United Nations can better support the government's efforts to tackle the internal challenges."

Ban said in a statement that he was deeply concerned about the fate of the girls and that "the targeting of children and schools is against international law and cannot be justified under any circumstances."

NTJ/MB