Lagos: The UN Security Council must impose sanctions on the Islamic extremists that abducted more than 300 schoolgirls, a leading Nigerian rights group said today, adding that expressions of concern and condemnation are not enough. The call comes as more experts are expected in Nigeria to help in the search, including US hostage negotiators. Nigeria`s government belatedly accepted offers of help last week from the United States, Britain, France, China and Spain amid mounting national and international outrage at its failure to rescue 276 girls abducted from a northeastern school on April 15. Fifty-three escaped. The militants are threatening to sell the girls into slavery. "The future of these missing schoolgirls hangs in a balance. The council should not leave them to fend for themselves," executive director Adetokunbo Mumuni of the Socio-Economic Rights and Accountability Project said in a statement. "But it is not enough for the Council to express concern ... It is now time for the council to act decisively against the Boko Haram. The cost of inaction is simply too high to contemplate." He said targeted sanctions would send a strong message. The United States already has designated Boko Haram a foreign terrorist organisation, as has the European Union, making it illegal to contribute to the group. And Washington last year put a USD 7 million ransom on the head of Boko Haram leader Abubakar Shekau, who said in a video last week that he will sell the girls into slavery.