Nigeria, Lagos (CNN) Negotiation talks between the Nigerian government and Boko Haram militants on the release of the remaining Chibok girls have been set back, President Muhammadu Buhari said.

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.

Unfortunately, the negotiations between the government and Boko Haram suffered some unexpected setbacks, owing mainly to a lack of agreement among their abductors, whose internal differences have led to a divergence of voices regarding the outcome of the talks. — Muhammadu Buhari (@MBuhari) April 13, 2018

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.

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