Shekau, who was not seen on camera for more than a year, released an unverified video late last month and said his time in charge of the Nigerian jihadist group may be coming to an end.
If the video indeed depicts Shekau, he appears thin and listless, delivering his message without his trademark fiery rhetoric.
It prompted speculation from the army that the Islamist group was on the verge of collapse in the face of a sustained military counter-insurgency.
However, in Friday’s message, Boko Haram maintained it was a potent fighting force, with fighters posing with AK-47s in front of Toyota Hilux pick-up trucks and a lorry mounted with a military cannon.
“You should know that there is no truce, there is no negotiations, there is no surrender,” an unidentified masked man wearing camouflage said in a prepared script in Hausa, in the video posted on YouTube.“This war between us will not stop.”
The video, which was of markedly better quality than Shekau’s and included Arabic subtitles, featured nine masked Boko Haram fighters standing on sandy ground in an undisclosed desert location.
It is unclear if the masked people in the video include the Boko Haram leader.Shekau was still the head of the “West African wing”, said the masked man in the video, likening Boko Haram to the Islamist insurgencies in Iraq, Libya and Syria.
In March 2015, Boko Haram pledged allegiance to the Islamic State group, another of the world’s most deadly terror organisations.
But there were few signs Boko Haram — now styled as Islamic State in West Africa Province (ISWAP) — has so far benefited from the partnership.
Nigeria’s army has since then won back swathes of territory from the militants, liberating thousands living under Boko Haram control.
An estimated 20,000 people have been killed since Boko Haram began its campaign of violence in 2009 to carve out a hardline Islamic state in northeast Nigeria.
More than 2.6 million people have fled their homes since then but some of the internally displaced have begun returning.