The president expressed "deep shock" and pledged "all the needed support" to the military to end the renewed threat, his office said late Saturday. The military statement issued overnight, nearly a week after the attack, didn't say how many soldiers were killed but it called the situation under control. Nigeria is often reluctant to expose casualty numbers after such attacks.
As Buhari faces growing pressure over insecurity ahead of next year's presidential election, aide Bashir Ahmad said the president had summoned military chiefs and sent the defense minister to neighboring Chad for an "urgent meeting" with President Idriss Deby. A multinational force combating Boko Haram is based there.
The Islamic State West Africa Province, the largest IS-linked extremist group in Africa and a recent offshoot of Boko Haram, claimed responsibility for the Nov. 18 attack in Metele in the northeast, according to the SITE Intelligence Group that monitors extremist messaging. The group last month caused outrage by killing an abducted health worker despite an urgent plea from the International Committee of the Red Cross to spare her life.
Nigerians are increasingly concerned about reports of growing casualties among troops fighting extremists. Buhari, who made the defeat of the Nigeria-based Boko Haram a major goal of his presidency when he was elected in 2015, "is preoccupied with re-election campaigns" while many homes are filled with mourners, human rights activist Okechukwu Nwanguma said in a statement on Saturday.
The government under Buhari, a former military dictator from the north, has claimed in the past that Boko Haram has been "crushed," but the extremists continue to carry out deadly suicide bombings and abductions in the northeast and wider Lake Chad region.
In an interview with The Associated Press last month, Nigeria's information minister Lai Mohammed said that "today not a single inch of our territory is occupied by Boko Haram" and that peace had largely returned to the northeast.
Associated Press writer Cara Anna in Johannesburg contributed.
Follow Africa news at https://twitter.com/AP_Africa