"We are trying to be careful. It is better to get our daughters back alive," Buhari said in a statement.
In April of that year, Boko Haram sparked international outrage when the militants captured 276 girls -- between the ages of 16 and 18 -- from a boarding school in Chibok. One-hundred three of the girls have been freed in two swaps with Boko Haram. But more than 100 of the girls remain in captivity, their whereabouts unknown.
Buhari is due to visit Yobe state this week as part of a "condolence and sympathy visits to (an) area where we have had unfortunate events," he said.
The Nigerian leader promised that his administration would continue to keep his citizens safe.
He also thanked the United States for its help in fighting the Boko Haram insurgency but called for more assistance in the areas of training and equipment, Buhari aide Femi Adesina said in a statement.
Buhari pledged free and fair elections in 2019. Recalling a visit from a previous secretary of state before the 2015 elections, he said that John Kerry "told the party in government then, and those of us in opposition, to behave ourselves, and we did."