Fighters from the Islamic State West Africa Province (ISWAP) attacked the convoy on Sunday in the town of Mainok outside the regional capital Maiduguri, killing troops and seizing weapons before storming a nearby base, the two sources said.

The attack was the deadliest this year against Nigeria's army which has been battling a decade-long jihadist insurgency in the region that has killed 36,000 people and displaced around two million from their homes.

"We lost 31 soldiers, including their commander who was a lieutenant colonel, in the ambush by the terrorists," a military officer said about the attack which happened around 1100 GMT.

The convoy was transporting weapons to Maiduguri when it came under attack, said a second military source who gave a similar toll.

"The terrorists came in several trucks, including four MRAPs (Mine Resistant Ambush Protected vehicles) and engaged the convoy in a fierce battle," the second source said.

The militants struck the convoy with rocket propelled grenades and overwhelmed soldiers, leading to the "colossal loss" of troops, he said.

The jihadists seized weapons and two MRAPs in the attack before descending on the base outside the town, the two sources said. The insurgents overran the base and partially burnt it along with several military vehicles.

Mainok, 50 kilometres (30 miles) from Maiduguri, has been repeatedly targeted by the jihadists.

ISWAP split from mainstream Boko Haram faction in 2016 and rose to become a dominant force in the northeast.