Six people, including four children, were killed on Saturday when an explosive device collected by metal scavengers exploded in northeast Nigeria's Borno state where troops are fighting jihadist groups, a local official and two anti-jihadist militia told AFP Sunday.

The home-made bomb went off when two metal scavengers were sorting through scraps they collected from the bush outside the town of Gubio, 80 kilometres from the regional capital Maiduguri, the sources said.

"Six people were killed in the IED (improvised explosive device) explosion, two men and four children who were pupils of an Islamic seminary near the scene," Mali Bulama, political administrator for Gubio district said.

The identity of the men had yet to be determined because they were badly mutilated by the blast that occurred inside an unfinished building used to store scraps, Bulama added.

Militia leader Babakura Kolo said the men were rummaging through heaps of metal when the device went off.

"The metal scavengers were sorting out the metals for possible objects of value when they brought out the IED from one of the sacks and it went off, killing them and four children playing nearby," Kolo said.

Umar Ari, another militia member, gave the same toll. The 14-year jihadist violence in the northeast has killed 40,000 and displaced around two million from their homes, forcing them to live in makeshift camps where they receive meagre food handouts from international charities.

Many of the displaced comb the landscape for firewood and metal scraps to raise money for food to supplement inadequate rations.

The loggers and scrap metal scavengers as well as farmers and herders are targeted by the jihadists who accuse them of spying on them for troops and militias fighting them.

Last June, Borno state authorities banned scrap metal collecting following an increase in jihadist attacks on the scavengers whom the authorities also accused of vandalising public property.

Despite the ban, scavengers continue their search amid risk of attacks by jihadists and explosion from unexploded ordnances.

In July 2022, 13 metal scrap collectors were killed and three others injured when an unexploded ordnance they excavated from the bush went off in the town of Bama near Sambisa forest, a jihadist enclave.