At least 70 bodies have been found in a mass grave in a Nigerian town recaptured from Boko Haram.
Troops form Chad and Niger said they found the bodies in Damasak, which was under the control of the militants for months.
Some of the victims are reported to have had their throats slit and others were decapitated, according to reports.
Chadian army Col Azem Bermandoa Agouna told AFP that he had visited the grave and seen "about 100 bodies spread under a bridge just outside the town".
Nigeria's President Goodluck Jonathan admitted the government was caught by surprise at the group's power.
"We never expected that [Boko Haram] will build up that kind of capacity. We under-rated their external influence. Since after the civil war we've not fought any war, we don't manufacture weapons, so we had to look for help to re-equip our army and the air force," he told the BBC.
But the president predicted the territories captured by the militants would be retaken in a month.
"They are getting weaker and weaker by the day," he said.
"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."