Chief of Army Staff Attahiru was just appointed by President Muhammadu Buhari in January as part of a shakeup of the top military command to better fight surging violence and a more than decade-long jihadist insurgency.

Attahiru died as news was also emerging that Nigeria's Boko Haram jihadist leader Abubakar Shekau had himself been seriously wounded or possibly killed after clashes with a rival Islamic State-allied faction.

President Buhari, a former general first elected in 2015, has been under increasing pressure from allies and critics alike over the mounting security problems in Africa's most populous country.

In a statement, Buhari said the crash "was one mortal blow to our underbelly, at a time our armed forces are poised to end the security challenges facing the country".

The army chief was killed when his aircraft crashed in the northern state of Kaduna, air force spokesman Edward Gabkwet told AFP, without giving any details about the incident.

Nigeria's military has been battling an Islamist insurgency in the northeast since 2009, a conflict that has killed more than 40,000 and displaced around two million more.

Attahiru had once been in charge of leading the frontline offensive against Boko Haram's Shekau in the northeast in 2017.

Local intelligence sources said Shekau had been seriously wounded this week when IS-allied rival jihadists attacked his stronghold in the Sambisa forest in the northeastern state of Borno.

Sources said Shekau was wounded when he shot himself to evade capture after militants from the Islamic State in West Africa Province (ISWAP) surrounded him following a series of battles between the rival groups.

Nigeria's army has said it is investigating the reports and neither ISWAP or Boko Haram have issued any statements about the Sambisa attack or Shekau's whereabouts.

But analysts said his loss would be a huge blow to Boko Haram and potentially allow the ISWAP faction to consolidate its territorial control in Nigeria's northeast.