Boko Haram on Sunday released a new video purportedly showing some of the Nigerian schoolgirls kidnapped by the jihadist group from Chibok more than two years ago.

The film was issued just days after embattled Boko Haram head Abubakar Shekau denied claims that he had been replaced as the leader of the Nigeria-based group.

The kidnapping of 276 schoolgirls from Chibok in April 2014 provoked global outrage and brought unprecedented attention to Boko Haram and its bloody quest to create a fundamentalist state in northeastern Nigeria.

A man whose face was covered by a turban in the video called on the Nigerian government to release Boko Haram prisoners in exchange for the girls.

"They should know that their children are still in our hands," he said in the film posted on YouTube.

While President Muhammadu Buhari has said the group is "technically defeated", his government has struggled to find the girls, an enduring political embarrassment that highlights Boko Haram's continued presence in the region.

The video was attributed to the original Boko Haram name, not the new Islamic State West Africa Province (ISWAP), suggesting it was released by Shekau's faction, although it is not known when it was filmed.

"There are a number of the girls, about 40 of them, that have been married," said the man in the 11-minute video, which shows girls with veils sitting on the ground and standing in the background.

"Some of them have died as a result of aerial bombardment."

A girl speaking in the Chibok dialect chokes back tears as she describes an aerial attack by Nigerian armed forces.

In the background, several girls look visibly distressed and dab their eyes as she recounts the raids. One is holding a small baby.

"They should immediately release our brethren in their custody," the man said, threatening that if the prisoners are not released that the Nigerian government will never be able to rescue the girls.

"This focuses on using the girls as a bargaining chip," Ryan Cummings, director at intelligence firm Signal Risk, told AFP.

"The video shows that the war effort is hurting the operations of the group," he said. "It does have a sense of almost desperation from Boko Haram."

In the hours that followed the April 2014 mass kidnap, dozens of girls managed to escape.

Of the 219 still missing, just one was found, Amina Ali, in May this year near the Sambisa Forest area of Borno, a known Boko Haram hideout.

Last week, Boko Haram's leader Shekau appeared in a video vowing to fight on, amid a leadership scuffle between him and new Islamic State-backed rival Abu Musab al-Barnawi.

Barnawi has criticised Shekau's indiscriminate and brutal leadership in Nigeria that has seen Boko Haram fighters kill thousands of people in mosques and markets and raze entire cities to the ground.

In March 2015, Shekau pledged allegience to the Islamic State and changed Boko Haram's name to ISWAP, prompting fears that the Nigerian insurgency would be bolstered by its connection to the international jihadist organisation.

Yet despite the official link, there have been few signs since the announcement that Boko Haram has benefited from the alliance, as the Nigerian military recaptures territory once controlled by the insurgents.

Over the past year, the Nigerian military announced the rescue of hundreds of people, most of them women and children, who have been kidnapped by Boko Haram.

But the missing Chibok schoolgirls were not among them, despite several unconfirmed sightings.

Abubakar Abdullahi, a spokesman for the Bring Back Our Girls movement, told AFP he had seen the video and that one of the girls has been identified.

"One of our members has recognised a girl. We are still in the process of confirming a few of the girls," Abdullahi said from Nigeria's capital Abuja.

Abdullahi said it was "heartbreaking" to see the video.

"We've always believed they will be back, but it's also painful," he said, criticising the Nigerian government for being unable to rescue the girls.

"The frustration will always be there. We failed them on so many instances," Abdullahi said.

"It's unbelievable that this can happen, that we haven't been able to make progress after 853 days."

Boko Haram has been blamed for some 20,000 deaths and displacing more than 2.6 million people since it launched a brutal insurgency in Nigeria in 2009 that has since spread into several neighbouring countries.