Nigeria's President Goodluck Jonathan has sacked his military high command, his spokesman Reuben Abati has said.
No reason was given but the dismissals come amid growing concern about the military's failure to end the Islamist-led insurgency in northern Nigeria.
Mr Abati said Air Marshal Alex Badeh replaces Admiral Ola Ibrahim as the new chief of defence staff, the most senior post in the military.
Boko Haram has been waging a four-year insurgency in Nigeria.
Mr Jonathan imposed a state of emergency in three northern states in May 2013, giving the military wide-ranging powers to end the insurgency.
'Tradition of sackings'
However, Boko Haram has continued with its campaign of violence - including attacks on two military barracks and an air base last month.
On Tuesday, the group carried out a car bomb attack in the north-eastern city of Maiduguri, killing at least 17 people.
United Nations figures suggest more than 1,200 people have been killed in Islamist-related violence since the state of emergency started.
Mr Abati said the new appointments would come into effect immediately.
The president had briefed the leadership of the National Assembly on the changes "and will, in keeping with the provisions of the law, request the National Assembly to formally confirm the appointments when it reconvenes", he added.
Mr Jonathan also appointed a new chief of army staff, replacing Lt Gen Azubike Ihejirika with Maj Gen Tobiah Minimah.
Rear Admiral Usman Jibrin takes over from Vice Admiral Dele Joseph Ezeoba as chief of naval staff and Air Vice Marshal Adesola Nunayon Amosu takes over from Air Marshal Badeh as chief of air staff.
BBC Nigeria analyst Naziru Mikailu says Mr Jonathan's decision does not come as a complete surprise because there is a tradition in Nigeria of sacking military chiefs.
It seems Mr Jonathan wants to show he is in charge, at a time when his leadership is being increasingly questioned within the governing People's Democratic Party (PDP) ahead of the 2015 elections, our correspondent adds.
Last month, ex-President Olusegun Obasanjo called on Mr Jonathan not to seek re-election, accusing him of failing to tackle Nigeria's many problems - including the Islamist insurgency, poverty and corruption.