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 Goodluck imposed a state of emergency in three northern states in May 2013, giving the military wide-ranging powers to end the insurgency.

However, Boko Haram has continued with its campaigning of violence - including attacks on military barracks.

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.