Lagos – The United Nations has reportedly told Nigerian authorities to work harder to find the remaining Chibok girls who were kidnapped by the insurgent group Boko Haram three years ago. According to Voice of America, the UN said in a statement it was shocked that most of the girls have still not been found. "It is deeply shocking that three years after this deplorable and devastating act of violence, the majority of the girls remain missing," several UN human rights experts were quoted as saying."As more and more time passes, there is a risk that the fate of the remaining girls will be forgotten. There must be more that the government of Nigeria, with the support of the international community, can do to locate and rescue them."This comes after the Bring Back Our Girls group earlier this month said the Nigerian government and military were not doing enough to ensure the release of the remaining 195 kidnapped Chibok schoolgirls. 3rd anniversary At the time, the group called for speedy negotiations to bring the remaining girls home before the third anniversary of the mass abduction that outraged the world.Friday, April 14 marks three years since the girls were taken by the insurgent group. The kidnapping of more than 200 schoolgirls from a northern Nigerian town hit international headlines and prompted global figures, including former US first lady Michelle Obama and a list of celebrities, to support the BringBackOurGirls campaign.None of the girls were seen again until May last year when one of the students, Amina Ali, was found in a forest with a baby and a man claiming to be her husband.Her discovery prompted hopes that the girls were alive, and Nigerian President Muhammadu Buhari pledged to ensure the release of the remaining girls in captivity. Following Amina's recovery, a group of 21 girls was released after Switzerland and the International Red Cross brokered a deal with Boko Haram.Those girls were briefly allowed to return to their homes to spend Christmas with relatives.But, after their brief freedom on Christmas Day, the girls were sent back to a secret location in the capital Abuja for debriefing by the Nigerian government.