The President of Chad has promised to "wipe out" Boko Haram, and claimed he knew where its leader is hiding, calling on him to give himself up.

"Abubakar Shekau must surrender. We know where he is. If he doesn't give himself up he will suffer the same fate as his compatriots," President Idriss Deby told a press conference yesterday.

"He was in Dikwa [north-eastern Nigeria] two days ago. He managed to get away but we know where he is. It's in his interests to surrender."

Deby went on to vow that Shekau's terrorist group, which caused the deaths of more than 6,000 civilians in 2014, would be defeated.

"We are going to win the war and we are going to wipe out Boko Haram, contrary to what certain media think. The Chadian and Niger forces will continue their mission to finally put an end to this shadowy group."

Nigeria's presidency declined to comment on Deby's remarks and a defence spokesman did not immediately respond to requests for comment.

Chad's army has waged a series of battles against Boko Haram as part of a cross-border military campaign and has re-taken territory the militant group held in north-eastern Nigeria.

The Chadian army is considered one of the best in the region, backed by a strong air force. It first deployed to help Cameroon fend off Boko Haram and is now pressing southwest into Nigerian territory after capturing the border town of Gambaru last month.

Nigeria's military has said on at least three occasions it had killed Shekau, or a man claiming to be him. Each time the leader has resurfaced to issue a fresh jihadist video, one of numerous videos the group has made.

A series of tweets from the Nigerian Army's Twitter account last September said that Shekau was "deceased" and a lookalike, Mohammed Bashir, who had allegedly been posing as the Boko Haram leader in recent videos, had also been killed.

This was later confirmed by military spokesman General Chris Okulade.

However, Boko Haram then released a video in which a man purporting to be Shekau ridicules the claims. "Here I am, alive. I will only die the day Allah takes my breath," he said, standing on the back of a pick-up truck and flanked by four heaving-armed masked militants. "Nothing will kill me until my days are over."

Terrorism experts have claimed that Boko Haram is "incorporating itself into the Islamic State," most noticeably through its propaganda videos.

A six-minute video posted on Twitter on Tuesday showing the beheading of two men bears resemblance to those posted by Islamists in the Middle East.

Veryan Khan, editorial director of the Terrorism Research & Analysis Consortium [TRAC], told Fox News that the latest release that IS supporters are "already starting to call Boko Haram the 'Islamic State Africa".

"Boko Haram is not a mere copycat of ISIS; rather, it is incorporating itself into the Islamic State," Khan warned.

(Additional reporting by Reuters)