The Boko Haram jihadist group released a video on Thursday claiming to show schoolboys seized in a mass kidnapping in northwest Nigeria last week.

The assault last Friday on a rural school in Kankara, Katsina state, was initially blamed on criminals, known as bandits, who have terrorised the region for years.

But on Tuesday Boko Haram claimed responsibility for the raid, which occurred hundreds of kilometres (miles) from its stronghold in northeast Nigeria -- the birthplace of a brutal decade-old insurgency.

A distraught teenager, speaking in English and Hausa in the video seen by AFP, said he was among 520 students taken by "the gang of Abu Shekau."

The teenager was surrounded by a large group of boys -- some looking very young -- who were clustered under a tree, appearing grubby and exhausted.

The video was released with a recording of a voice ressembling that of the group's elusive leader, Abubakar Shekau, behind the 2014 abduction of 276 schoolgirls in Chibok that sparked global outrage.

It reiterated Boko Haram's claim of responsibility.

Several hundred boys were taken in the mass abduction
Several hundred boys were taken in the mass abduction AFP / Kola Sulaimon

"I earlier released an audio confirming our people did God's work, but people denied it," the voice said. "Here are my men, and your children have spoken."

The video was sent to AFP via the same channel as previous messages by Boko Haram.

The government has not immediately reacted to the group's claims, nor confirmed the exact number of children missing.

Two accounts by different officials have put the number of schoolboys at 320 or 333.

Security sources told AFP Wednesday that the operation was carried out on Boko Haram's orders by a notorious local gangster called Awwalun Daudawa, in collaboration with Idi Minorti and Dankarami, two other crime chiefs with strong local followings.

Experts recently warned of attempts by jihadists to forge an alliance with criminal gangs in the northwest.

Many parents of the missing students in Kankara said they had long feared an attack, given escalating violence in the region.

The boys were kidnapped from Kankara
The boys were kidnapped from Kankara AFP / Robin BJALON

"Our children told us armed men would come up to the school fence but they never breached the fence... until last Friday," Hauwa'u Isah, mother of an abducted child said.

Around 8,000 people have been killed in the northwest since 2011, according to the International Crisis Group (ICG) think tank.

#BringBackOurBoys started trending on social media, in reference to a similar hashtag after the Chibok kidnappings.

Small protests to push for the boys' release took place in Katsina on Thursday as President Muhammadu Buhari was visiting the state.

"Why we are here today is because we want to tell the Federal Government that what they are doing is not enough," protester Jamilu Aliyu Turanci said.

"Mr President has failed us."

The governor of Katsina state, Aminu Bello Masari, said late Monday that the abductors "have made contacts with the government."

"Talks are ongoing to ensure their safety and return to their respective families," he said on Twitter.

Parents have been gathering at the school daily since the abduction, desperate for any information about the children's fate.

"I was about to leave yesterday evening when a boy who escaped was brought here," said one mother Murja Goma.

"He said they had no food to eat, that they live on leaves and acacia fruit that their captors pluck from the trees for them.

"We have shed so much tears, our hearts are grieving and we don't even know what to do," the woman said, appealing to the government to rescue the children.