Fighters from Islamic State West Africa Province (ISWAP) on Friday used explosives and guns to attack a column of more than 30 troops on foot patrol outside the town of Damask near the border with Niger, the sources said.

"We lost nine soldiers in an ambush by ISWAP terrorists and many others are still missing," a military officer said.

The soldiers, who were 25 kilometres (15 miles) from their base, dispersed in all directions following sustained gunfire from the jihadists, said the officer who asked not to be identified.

"The terrorists detonated an explosive device they had planted on the road in advance, increasing the casualties and confusion among the soldiers," he said.

Eight soldiers managed to return to base while the rest remain missing, including their commander with the rank of a major, the officer said.

"A man who identified himself as an ISWAP terrorist keeps answering the call to the commander's mobile phone, suggesting he is in the hands of the terrorists," he added.

Ya-Mulam Kadai, a spokesman for government-funded anti-jihadist militia assisting the military in Damask, gave the same casualty toll.

The nine bodies of the slain soldiers were recovered by a military search team deployed at the scene of the attack, he said.

The military did not respond to AFP's request for comment.

The Nigerian military has in recent weeks intensified ground operations against ISWAP, particularly in its Sambisa forest stronghold, with the military making regular claims of killing huge numbers of jihadist fighters.

ISWAP and rival Boko Haram factions have been attacking military targets, raiding bases, laying ambush and planting explosives against patrols on highways.

Nigeria's insurgency has killed more than 40,000 people and displaced around two million in the northeast since it erupted in 2009, according to the United Nations.

The conflict has spilled into neighbouring Niger, Cameroon and Chad, leading the region to launch a military coalition to fight the jihadist groups.