Nigeria's army claimed victory Wednesday in "a fierce battle" in a remote desert trading post where Islamic extremists said they killed 40 troops from a multinational force.
Army spokesman Col. Sani Kukasheka Usman said troops recaptured Malam Fatori town on Tuesday and killed several extremists, but the insurgents regrouped at the nearby border with Niger.
The Islamic State's West Africa Province, one faction of the Boko Haram extremist group, hours earlier claimed it had annihilated "a convoy of the African Coalition Crusader forces" at Malam Fatori, killing more than 40 soldiers and wounding dozens, according to the SITE Intelligence Group, which monitors extremist communiques.
There was no way to independently verify either side's claim.
Tuesday's battle was the first Nigeria attack claimed by the Islamic State group since August, when it named a new caliph in Nigeria, provoking a leadership struggle. Leader Abubakar Shekau pledged Boko Haram's allegiance to IS in 2015, giving the Islamic State its first sub-Saharan franchise. But IS last month announced it had replaced Shekau in a dispute around his indiscriminate killings of Muslims.
The town of Malam Fatori has changed hands many times in the seven-year Boko Haram uprising that has killed more than 20,000. Many residents fled to Niger in 2014 after soldiers in a punitive raid burned down hundreds of huts because a wounded extremist was given refuge there.
Tuesday's was the fourth insurgent attack in northeast Nigeria in three days.
Eighteen people were killed Sunday and Monday when extremists gunned down Christians leaving a church service, beheaded a village head and his son and ambushed a convoy within miles of Maiduguri, the biggest city in the northeast.
No one has claimed responsibility for those attacks.