The new Chief of Army Staff, Major General Ibrahim Attahiru has officially resumed duty.
He resumed officially after a hand over ceremony at the Defence Headquarters in Abuja, on Wednesday.
But human rights lawyer Femi Falana says Buhari cannot appoint service chiefs without legislative approval. Falana says the president can only nominate security chiefs who must then be confirmed by lawmakers before assuming office.
Nevertheless, Attahiru takes over from Lieutenant General Tukur Buratai who resigned Monday.
Following the retirement of the immediate past service chiefs, President Muhammadu Buhari had approved the appointment of their replacement.
The new service chiefs include, Major-General LEO Irabor, Chief of Defence Staff; Major-General I. Attahiru, Chief of Army Staff; Rear Admiral AZ Gambo, Chief of Naval Staff and Air Vice-Marshal IO Amao, Chief of Air Staff.
Addressing the new service chiefs, Buhari had charged them to be patriotic in the discharge of their duties.
The president had disclosed that Nigeria was in a state of emergency, hence the new service chiefs should serve Nigeria well.