He gave no reasons for the resignation of the army, navy and air force commanders, who he appointed in 2016.
But he tweeted the names of the replacements.
I have also appointed new Service Chiefs, to replace the retired officers:
Major-General Leo Irabor, Chief of Defence Staff
Major-General I. Attahiru, Chief of Army Staff
Rear Admiral A.Z Gambo, Chief of Naval StaffLoading...
Air-Vice Marshal I.O Amao, Chief of Air Staff.
— Muhammadu Buhari (@MBuhari) January 26, 2021
Governors and the National Assembly had called on Buhari to replace the military chiefs as they said they were underperforming.
Buhari, a former army general, was elected on a pledge to end insurgency in the northeast of the country, where the Islamist group Boko Haram operates.
While in the northwest, kidnappers are active.
In December some 300 schoolboys were kidnapped and later returned to their home. Authorities said local bandits were responsible.
In central regions, clashes between farmers and cattle herders have worsened.
The Boko haram insurgency has long plagued the country and put pressure on the government as security issues mount.
Large parts of the country are out of government control and an offshoot of Boko Haram – the Islamic State in West Africa Province group- has become even deadlier in the northeast.
Since 2009, at least 36,000 people have been killed in armed conflicts and millions have been displaced.
The violence has spread to neighbouring Niger, Chad and Cameroon.