"It is with a heavy heart that I regretfully announce the unfortunate demise of former Chief of Defence Staff, Air Chief Marshal Alex Sabundu Badeh", air force spokesman Ibikunle Daramola said in a statement late Tuesday.

Badeh, 61, died Tuesday "from gunshot wounds sustained when his vehicle was attacked while returning from his farm along Abuja-Keffi road".

The air force did not say if any arrests had been or suggest motives behind the killing.

Badeh who served as Nigeria's defence chief under former president Goodluck Jonathan, retired in 2015.

He has been on trial since his retirement over allegations of corruption while in office.

Nigeria, Africa's most populous country, is battling a myriad of security problems, from Boko Haram jihadist insurgency in the northeast to farmer-herder conflict in the centre and kidnappings for ransom ans armed robberies in the south.

President Muhammadu Buhari who came to power in 2015 and is seeking a second term in February elections, has come under fire for not doing enough to address the security challenges.