Hundreds of bodies, including women and children, have been found dead in the northeast Nigerian town of Damasak, apparently victims of Boko Haram fighters, local residents have said.
Reports of decomposing bodies littering the streets of Damasak came as president Muhammadu Buhari denounced Boko Haram as a bogus religious group and vowed a hard line against its fighters when he takes office at the end of next month.
The grim find in Damasak "far outnumbered" that of about 100 bodies found in a mass grave under a bridge after the town was liberated in early March by Chadian forces, said local resident Kaumi Kusur, the AFP news agency reported.
"Dead bodies were found in houses, streets and many more in the Damasak River which has dried up," he said, adding the victims were buried in 20 mass graves at the weekend.
The northeastern states of Adamawa, Borno and Yobe have been relentlessly targeted throughout Boko Haram's six-year uprising but there had been a lull in violence in recent weeks.
A coalition of troops from Chad, Cameroon, Niger and Nigeria has claimed major victories since February, reportedly flushing the fighters out of areas they previously controlled.
Boko Haram opposes Western education and wants to impose Islamic law in all 36 states of Nigeria, which is roughly equally divided between a predominantly Muslim north and a mainly Christian south.
The discovery of the bodies in Damasak appeared to underline both the brutality of the conflict and the continuing threat posed by the fighters.
Bodies covered by sand
Mohammed Sadiq, another local who helped in the burials on Saturday, put the death toll at more than 400 but the Borno state government did not state a precise figure, giving a toll of "hundreds".
The victims had been covered by sand from the encroaching desert, with the burial ordered by the state authorities, which are looking at the return of thousands of people displaced by the violence.
Buhari, who takes office on May 29, was elected last month on a pledge of a tougher approach to Boko Haram than the current administration of President Goodluck Jonathan.
The former military ruler said in a statement issued by his All Progressives Congress party: "No religion allows for the killing of children in school dormitories, in markets and places of worship.
"They have nothing to do with religion. They are terrorists and we are going to deal with them as we deal with terrorists."
Buhari was speaking after Boko Haram fighters stormed the island of Karamga on Lake Chad in motorised canoes before sunrise on Saturday.
Troops from Niger stationed on the island "were caught off guard" and suffered heavy losses, said Umar Yerima, a fisherman who witnessed the raid but escaped by hiding in long grass near the shore.
Niger's military confirmed the attack but did not provide a death toll.
A security source in Chad said Niger lost 48 soldiers and another 36 were missing.