Nigeria's army said Thursday it was trying to verify the authenticity of a video that appeared to show Boko Haram's leader mocking reports that he may have been killed.

A security task force last month said wanted Islamist insurgent commander Abubakar Shekau "may have died" from a gunshot wound after a clash with soldiers on June 30.

In a video seen by AFP Wednesday, a man resembling past images of Shekau taunted the regional military spokesman who suggested he had been killed.

"We cannot say at this juncture whether the claim is true or false until we authenticate the veracity of the video," army spokesman Ibrahim Attahiru told AFP.

"The army authorities have to verify the claim. This is precisely what we are doing," he said.

The initial statement concerning Shekau's possible death came from a military spokesman based in the northeast, Boko Haram's stronghold.

National defence spokesman Chris Olukolade has told AFP that statement may have been issued prematurely and that the military lacked definitive proof of Shekau's death.

Shekau has been declared a global terrorist by the United States, which put a $7 million bounty (5.2 million euros) on his head.

He leads an Islamist group which has been blamed for scores of deadly attacks across northern and central Nigeria.

It was not clear when or where the latest video was recorded, but in it Shekau claims recent attacks in the northeast.

"I want the whole world to know that I'm alive by the grace of Allah," he says in the Hausa language.

Boko Haram has said its four-year insurgency is aimed at creating an Islamic state in Nigeria's mainly Muslim north.

Nigeria in mid-May imposed a state of emergency across most of the restive northeast and launched an ongoing offensive aimed at crushing the insurgency.