One army officer and 10 soldiers were killed in Nigeria's Benue state in what a spokesman said was an unprovoked attack on Thursday.

The Nigerian army said in a statement that it would "fish out and deal decisively with these bad elements."

Civilians, in fear of soldiers looking to root out the perpetrators, were fleeing the Konshisha local government where one local leader's house had been burnt to the ground, sources told Reuters.

The violence in the restive Middle Belt region marked the latest bout of instability in Nigeria, Africa's most-populous nation.

On Monday, heavily armed gunman freed more than 1,800 prisoners in the southeast, while armed gangs have kidnapped hundreds of school children in the northwest in recent months and Islamist militants in the northeast have waged a decade-long insurgency.

Troops patrol in the Middle Belt due in part to clashes between farmers and nomadic cattle herders that have killed thousands and displaced half a million over the past decade, according to estimates from French medical charity Medecins Sans Frontieres.

Army spokesman Mohammed Yerima said the troops were initially declared missing while on a routine operational task, but a search-and-rescue team later found the bodies.

"Efforts are ongoing to track down the perpetrators of this heinous crime with a view to bringing them to justice," Yerima said in a statement.

Yerima did not immediately reply to further queries about the attack.