Troops killed 28 suspected militants during a weekend operation in central Nigeria launched in response to an attack last month which saw six soldiers gruesomely murdered, the military said Monday.

The violence occurred on the border between Plateau and Taraba states, an area plagued by waves of sectarian violence seen as separate from Boko Haram, although the Islamist insurgents have claimed past attacks in the region.

"In our effort to rid the border communities... of incessant killings and brigandage, there was an exchange of fire between troops and militiamen in which lives were lost," military spokesman Ikedichi Iweha told AFP, referring to Saturday's unrest.

"Twenty-eight members of the militia group lost their lives, one soldier was injured while another is still missing following the battle," he added.

Iweha said the offensive in the districts of Wase and Langtang was launched in response to an April 28 attack by militants on troops operating in the area.

"They killed the soldiers, took away their arms, gorged out their eyes, cut their tongues and decapitated their bodies in a most horrible manner," he added.

He fiercely denied accusations circulating in local media that the troops went on a rampage, indiscriminately firing on defenceless civilians in retaliation for the six soldiers' gory deaths.

Plateau state government spokesman Pam Ayuba said locals on his side of the border were angry their community was targeted in the operation, as the purported militants were clearly based in Taraba.

There was no immediate indication as to the identity of the suspected militants and it was not clear if they had any connection to Boko Haram.

Iweha said the search for the attackers was ongoing.

Plateau state falls in Nigeria's so-called Middle Belt, where the mainly Christian south meets the majority Muslim north.

Christian-dominated farming communities have clashed with largely Muslim herdsmen of the Fulani ethic group since the turn of the century, leaving thousands dead.

Ayuba said the region on the Taraba border has been peaceful for several years.

Violence by Boko Haram has most heavily been concentrated in Plateau's capital Jos, where churches and markets have been repeatedly bombed.

Most violence in rural areas has been blamed on long-standing sectarian grievances fuelled partly by battles over land rights.