Soldiers from Niger and Chad made a gruesome discovery on Friday outside Damasak in neighbouring Nigeria.
At least 70 bodies were found near a bridge outside of the town, which had been recently freed from the grips of Nigerian terrorist group Boko Haram.
Witnesses told Reuters that some of the bodies had been beheaded, and were skeletal and partially mummified.
Damasak fell to Boko Haram in November, but was reclaimed by Nigerien and Chadian soldiers on Saturday.
The countries, along with Cameroon, are part of a coalition fighting to break Boko Haram's grip on the region.
The discovery of the bodies came just after Nigerian President Goodluck Jonathan boasted that terrorists "are getting weaker and weaker by the day," and predicted territories would be reclaimed by the government in the coming weeks.
"I'm very hopeful that it will not take us more than a month to recover the old territories that hitherto have been in [Boko Haram's] hands," he told the BBC on Friday.
The Sunni Muslim extremists have led a reign of terror across Nigeria with increasing brutality over the past five years, with kidnappings, suicide bombings, and mass executions leaving thousands dead and millions displaced.
Boko Haram became internationally known after kidnapping over 270 children from an all-girls school in Chibok, Nigeria on April 14, 2014. A second mass kidnapping occurred on May 4 in Warabe. Over 200 girls remain missing, but President Jonathan expressed confidence that they will be found alive.
"We have not seen dead girls, that is the good news," he said this week. "I believe they are still alive, I believe we will get them."
BBC reported that civilians in neighbouring countries have not joined up with the Nigerian-based terrorists, stifling the group's goal of creating a caliphate.
