Nigerian President Muhammadu Buhari on Monday sacked his entire military top brass, his spokesman said, in a widely expected move as he wrestles with an insurgency by Boko Haram extremists.

Nigerian President Muhammadu Buhari on Monday sacked his entire military top brass, his spokesman said, in a widely expected move as he wrestles with an insurgency by Boko Haram extremists.

"The President has relieved the service chiefs, including the heads of the army, air force and navy of their appointments," Femi Adesina told AFP.

Chief of Defense Staff Alex Badeh and the National Security Adviser (NSA) Sambo Dasuki were also sacked, a separate statement from Buhari's office added.

"President Buhari thanks the outgoing Service Chiefs and National Security Adviser for their services to the nation and wishes them well in their future endeavors," it added.

Major-General Abayomi Gabriel Olonishakin was named new Chief of Defense Staff while Major General Tukur Yusuf Buratai becomes the new army chief, according to the statement.

Buratai, who comes from Borno state -- the worst affected by the insurgency -- has been commander of the new, strengthened regional force against Boko Haram which is due to deploy later this month.

A new commander for the multi-national force will now be appointed, Adesina said.

Rear Admiral Ibok-Ete Ekwe Ibas was appointed to head the navy while Air Vice Marshal Sadique Abubakar becomes chief of air staff.

Air Vice Marshal Monday Riku Morgan is the new Chief of Defense Intelligence while retired Major General Babagana Monguno replaces Dasuki as NSA.

All the appointments have to be confirmed by Nigeria's Senate.

Badeh and the former army, air force and naval chiefs were appointed by former president Goodluck Jonathan in January 2014, a month after he sacked the previous top brass.

That followed a daring raid against a military installation in the northeastern city of Maiduguri, which saw aircraft destroyed and weapons seized.

The military command has come under heavy criticism for its poor handling of a six-year insurgency that has killed 15,000 people and forced 1.5 million to flee their homes.

On the commanders' watch, the militants captured swathes of territory, including towns and villages in the remote northeast in its quest to establish a hardline ISIL.

In addition, the sacked military chiefs were unable to free more than 200 schoolgirls abducted in the northeastern town of Chibok in April 14 last year, despite repeated promises.

Boko Haram has stepped up its attacks since Buhari became president on May 29, with a wave of raids, explosions and suicide bombings against civilians.

Some 570 people have been killed in Nigeria alone, according to AFP reporting.

The surge in violence has sparked concern that gains made by the armies of Nigeria, Niger, Chad and Cameroon against the militants since February this year are being eroded.