The jihadist group Boko Haram has released a new video without its embattled leader Abubakar Shekau, lending weight to claims by the Nigerian army he had been gravely wounded in an air strike.

The 13-minute video posted on YouTube late Tuesday shows an unidentified man in a flowing white robe and a sword dangling by his side presiding over Eid prayers in a mosque.

Hundreds of poorly fed villagers and children, who are apparently Boko Haram supporters, are seen in the video filmed on Monday.

The man says he is representing Shekau, who had allegedly been ousted by the Islamic State to which Boko Haram pledged allegiance in March 2015.

"My brethren, today is Eid ..in the Islamic Caliphate under the leadership of Abubakar Shekau, may Allah protect him," he says, speaking in the local Hausa language.

The Nigerian army claimed on August 23 Shekau had been seriously wounded in the shoulder in an air raid in which several commanders were killed.

"We convey our Eid greetings to our brethren all over the world under the Islamic Caliphate and especially our leader Abubakar Shekau, may Allah protect him," the man in the video says.

- 'No retreat, no surrender' -

He then taunts the government of President Muhammadu Buhari, saying Boko Haram would fight on despite a military crackdown, adding: "No retreat, no surrender."

It was not immediately clear if the video, which was technically superior to previous ones, was shot in Boko Haram's Sambisa forest stronghold in the northern state of Borno or elsewhere.

Nigerian soldiers, with the support of regional troops, have recaptured swathes of territory lost to the jihadists since they launched a military campaign in February 2014.

Despite earlier claims by the Nigerian government that Shekau had been killed, the militant leader has resurfaced later in videos.

Last month, the IS replaced Shekau with Abu Musab al-Barnawi, the son of Boko Haram founder Mohammed Yusuf, in an apparent split in the group whose insurgency has killed some 20,000 and displaced more than 2.6 million since 2009.

Boko Haram has also released a video showing at least one of the more than 200 schoolgirls kidnapped from Chibok more than two years ago, and called for its detained fighters to be freed.

The mass kidnapping of schoolgirls from the remote town of Chibok provoked global outrage and brought unprecedented attention to Boko Haram and its bloody quest to create a fundamentalist state in northeastern Nigeria.

Nigeria is facing security threats on multiple fronts: Boko Haram Islamists in the northeast, Biafran separatists in the southeast, oil rebels in the south and nomadic herdsmen in the central states.