Shekau, is notorious for suicide bombings and indiscriminate killings of civilians.

Shekau has pledged allegiance to ISIS leader Abu Bakr Al-Baghdadi, but ISIS central gave its formal backing to the Barnawi faction, which is known as Islamic State West Africa Province.

ISWAP has lately intensified its armed campaign, launching a number of major assaults on military targets in Borno and neighbouring Yobe state amid signs of a takeover by more hardline leaders.

There have been more than 20 attacks on military bases since July, with at least nine so far this month. Most of the attacks have been blamed on ISWAP, or claimed as ISWAP attacks by ISIS.

On December 14, Nigerian soldiers were killed in roadside bomb blast near Gamboru.

Boko Haram fighters attacked a military base in Gulumba killing at leasttwo soldiers on December 8. The attack involved a suicide bomber, a hallmark of the Shekau faction.

Three civilians were killed in fighting between troops and ISWAP in Jakana on December 7.

Two military bases were attacked in the Rann and Bama areas of Borno on December 6 and 7.

On December 4, ISWAP fighters launched an assault on a military base in Gudumbali, sparking a fierce firefight in which two soldiers were injured.

ISWAP fighters attacked a military base in Mallam Fatori near the borders with Niger and Chad on December 3. One soldier was killed and several others were injured in the attack.

On December 1, an ISWAP attack in the Yobe state village of Buni Gari left eight soldiers dead, the Nigerian army said, while ISIS claimed ISWAP fighters killed