At least 10 Nigerian soldiers have been killed and nine severely injured in an ambush by jihadists in restive northeast Nigeria, military sources said on Thursday.
Another 12 soldiers were missing after a column of troops on patrol was ambushed by the fighters on Wednesday in Damboa district of Borno state, a military officer told AFP on condition of anonymity.
Fighters loyal to the Islamic State group claimed responsibility for the killings, but said they had slain 22 soldiers after an assault by the army.
A decade-long jihadist insurgency in northeast Nigeria has killed 35 000 people, displaced two million others and spilt into neighbouring countries.
"We lost 10 troops in the intense fighting with the terrorists who ambushed our soldiers conducting a clearance operation in the area," said the officer, who asked not to be identified because he was not authorised to speak about the incident.
"Nine soldiers were injured and 12 are still missing."
The troops came under attack while returning to their base in Damboa, 88km from the state capital Maiduguri, said a second military officer who gave the same casualty toll.
Soldiers were forced to withdraw after an hour-long battle in which nine jihadists were also killed, said the second source.
The source said militants burnt five military vehicles and took away a pickup truck along with six machine guns.
The military sources initially attributed the attack to the Boko Haram faction led by long-time leader Abubakar Shekau as it took place close to its stronghold in Sambisa forest.
But the killings were later claimed by rival jihadists loyal to the Islamic State group.
A statement released by ISIS propaganda arm Amaq said the faction's fighters had killed 22 troops after the Nigerian army attacked them.
Boko Haram has splintered into two major factions: one loyal to Shekau and the other aligned to IS.
There has been a lull in attacks on troops from the jihadist factions in recent weeks as the military has intensified operations against the fighters.
According to security sources, jihadists have been forced to flee into Cameroon and Chad or hide in camps on several islands in Lake Chad.
Attacks on Nigerian troops had increased since June last year, with most of the deadly assaults blamed on or claimed by the Islamic State West Africa Province (ISWAP) faction.
ISWAP split from Boko Haram in 2016 and focuses on attacking military targets while Boko Haram is notorious for attacks on civilians.
On Tuesday, Mai Mala Buni, the governor of Yobe, one of three northeast Nigerian states beset by the jihadist conflict, called for dialogue with the fighters to help end the violence.
"No conflict of this nature anywhere in the world has been resolved solely by military means," he told a security gathering.
"We therefore suggest that we should seek - and use - back channels to open communications and contacts that both sides could trust as credible."