At least 70 bodies were found in a mass grave on the outskirts of the town of Damasak after it was recaptured from Boko Haram fighters, Chadian and Nigerien military officials have said.

Soldiers discovered the bodies, some decapitated, under a bridge just outside the town on Friday, which was retaken from Boko Haram by troops from Chad and Niger.

"There are ... bodies spread around under the bridge just outside the town," Colonel Azem Bermandoa Agouna told the AFP news agency, adding that he had visited the scene himself close to the border with Niger.

He claimed the massacre probably happened about two months ago and blamed it on the Boko Haram armed group from Nigeria.

Footage showed the bodies were strewn beneath the concrete bridge on one of the main roads leading out of the town.

Colonel Bermandoa Agouna told AFP that several of the victims had been decapitated while others had been shot. "There are heads here and bodies there, the mass grave has become like a termite mound," he added.

A Reuters news agency military source also claimed that the bodies were Boko Haram's victims.

Al Jazeera cannot independently verify these claims.

Chad and Niger launched a vast air and ground offensive against Boko Haram in the area on March 8, quickly taking Damasak from the group.

"Operation Mai Dounama" aims to destroy Boko Haram bases close to Niger, a Nigerien army spokesman said on Thursday.

Damasak was seized by the group in November killing around 50 people and forcing another 3,000 to flee, according to the UN's High Commissioner for Refugees. But the town was recaptured by African troops on Saturday.

Boko Haram has killed thousands of people in six years of fighting aimed at establishing an Islamic caliphate in northeast Nigeria. 

Source: Agencies