Kano, Nigeria: At least 10 Nigerian soldiers have been killed and nine severely injured in an ambush by suspected Boko Haram fighters in restive northeast Nigeria, military sources said Thursday.

Another 12 soldiers were missing after a column of troops on patrol was ambushed by the extremists on Wednesday in Damboa district of Borno state, a military officer told AFP on condition of anonymity.

“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 decade-long extremist insurgency in northeast Nigeria has killed 35,000 people, displaced two million others and spilt into neighbouring countries.

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.

The area of the attack is on the edge of the Sambisa Forest which is a stronghold of the Boko Haram faction led by long-time leader Abubakar Shekau.

Soldiers were forced to withdraw after an hour-long battle in which nine extremists were also killed, said the second source.

The militants burnt five military vehicles and took away a pickup truck along with six machine guns.

Troops destroyed one extremist truck and recovered three Kalashnikov rifles, he said.