Nigeria's President Muhammadu Buhari has appointed new defence chiefs after sacking the heads of the army, navy and air force, BBC reported Monday.

The sackings were expected as the president has repeatedly criticised the military's inability to defeat Boko Haram.

The Islamists have recently launched a series of deadly guerrilla attacks, killing more than 250 people.

Boko Haram is thought to be responsible for more than 10,000 deaths since 2009.