Boko Haram fighters attacked Nigerian troops early on Monday, the army said, after two suspected suicide bombers were shot dead near military positions.
Army spokesman Sani Usman said in a brief emailed statement: “Boko Haram terrorists attack troops of 113 Battalion at Kareto, northern Borno state.
“The troops have been battling the insurgents since the early hours of today.”
A soldier with the regiment told AFP the troops were ordered to the town of Damasak near the border with Niger and took up position in Kareto, some 38 kilometres (24 miles) away.
“Today at about 6:30 am (0530 GMT), two suicide bombers approached us and we shot at them and they exploded,” he said.
“As soon as the explosives went off, there were barrages of heavy artillery fired by Boko Haram, who came in large numbers with heavy weapons.
“We took up position in our trenches and fired back but they kept firing RPGs (rocket-propelled grenades), which we didn’t have.
“We lost some men, I don’t know how many, and many others were injured. Some of us fled in disarray. We realised that we were outnumbered and outgunned.”
The troops withdrew to Jeyimolo village and a fighter jet was deployed to Kareto while a search was launched for the dead and missing, he added.
A local chief confirmed the attack but said further details were still sketchy.
President Muhammadu Buhari said in December the Islamist militants had been weakened to the extent they could no longer mount conventional attacks against the military.
But the latest strike again underlines the persistent threat posed by the Islamic State group affiliate, particularly in hard-to-reach rural areas