A disagreement between members of the terror group is responsible for the breakdown in negotiations, Buhari said in a statement Friday."Unfortunately, the negotiations between the government and Boko Haram have suffered some unexpected setbacks, owing mainly to a lack of agreement among their abductors." Buhari said.This statement comes as Nigeria marks the four-year anniversary of the abductions in which militants seized 276 girls from a boarding school in Chibok town in Borno state, sparking a global outrage.Some of the girls were freed last year following negotiation talks between the Nigerian government and Boko Haram.However, more than 100 Chibok girls remain in captivity four years later.Bring Back Our Girls group which has long campaigned for the safe return of the girls, marked the anniversary on Saturday with a march in Lagos and a lecture given by Tunde Bakare, a prominent cleric in Nigeria's capital Abuja. President Buhari said though it has taken so long to secure their release, government was doing its best to free the remaining Chibok girls from their abductors.He said the return of over 100 schoolgirls kidnapped by Boko Haram from Dapchi, a town in Nigeria's Yobe State should reassure parents in Chibok that their daughters will return home."We know that this is not the news you parents want to hear after four whole years of waiting, but we want to be as honest as possible with you. "However, this government is not relenting," Buhari said.Boko Haram has kidnapped more than 1,000 children in Nigeria since 2013, a UNICEF report said Friday, most recently kidnapping 110 schoolgirls from the town of Dapchi in Yobe state on February 19.All of the girls have now been reunited with their families after they were freed by the terror group last month.However, one of them Leah Sharibu remains in captivity because she allegedly refused to renounce her Christian faith.