Boko Haram leader Abubakar Shekau has appeared in a new video to challenge a claim by the Nigerian president and the army that the armed group had been routed from its last stronghold of Sambisa Forest .

Al Jazeera reports that Shekau last appeared in a video in September where he disputed a claim by the Nigerian military that he had been wounded in battle.

“We are safe,” he says  in the 25-minute video, flanked by masked armed fighters, which appeared on Thursday.

“We have not been flushed out of anywhere. And tactics and strategies cannot reveal our location except if Allah wills by his decree.”

Referring to Nigerian President Muhammadu Buhari, who said on Christmas Eve that Boko Haram had been defeated and driven away from the forest, its last known bastion, Shekau says: “You should not be telling lies to the people.

“If you indeed crushed us, how can you see me like this? How many times have you killed us in your bogus death?”

It was not immediately clear where the new video was shot, but Shekau, who spoke in both Hausa and Arabic, said it was filmed on Christmas Day.

He pledged to continue fighting on until an Islamic state is imposed in northern Nigeria.

“Our aim is to establish an Islamic Caliphate and we have our own Caliphate, we are not part of Nigeria,” he says.

Buhari had announced that a sustained military campaign in the 1,300sq km Sambisa Forest in northeastern Borno state had led to the “final crushing of Boko Haram terrorists in their last enclave in Sambisa Forest”.

The government in Abuja and the military frequently claim victories against Boko Haram.

Speaking to Al Jazeera, Brigadier-General Victor Ezugwu, a Nigerian army commander, said his soldiers had made significant gains against Boko Haram.

The army has claimed victory over Boko Haram in its stronghold, having captured the Sambisa Forest in the country’s east over the weekend. The Nigerian army described the video as a propaganda which is aimed at causing fear.

“We are on top of the situation, all hands are still on deck,” Ezugwu told Al Jazeera. “This defeat is final and it [Boko Haram] will not spread to other parts of West Africa