More than 100 bodies have been found in a mass grave in northeast Nigeria after a town was reclaimed from Boko Haram terrorists.

The bodies - many with their throats slit and heads cut off - were found underneath a bridge in the town of Damasak, after it was retaken earlier this month by troops from Chad and Niger.

It is believed the victims may have been killed more than two months ago, due to the fact the bodies were severely decomposed.

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Brutal: Abubakar Shekau, leader of the Islamist extremist group Boko Haram, preaching his messages of hate. The insurgents have lost ground to army forces in recent weeks

Victory: Chadian soldiers celebrate after reclaiming the town of Damasak. They were later horrified to find a mass grave outside of the town where more than 100 bodies had been dumped

Colonel Azem Bermandoa Agouna said several of the victims had been decapitated, while others had been shot.

He said: 'There are about 100 bodies spread around under the bridge just outside the town.

'There are heads here and bodies there, the mass grave has become like a termite mound.'

He claimed the massacre probably occurred about two months ago and added: 'This is the work of Boko Haram.'

The Islamist uprising, which initially began as a campaign against Western education, has claimed more than 13,000 lives since 2009.

In a recent chilling development, the sinister group recently allied themselves with the Islamic State terrorists in Syria and Iraq.

Pledge: A Boko Haram flag flutters from an abandoned command post in the town of Gamboru. The terror group recently pledged allegiance to the Islamic State

Chad and Niger launched an intensive ground and air offensive against Boko Haram in the area earlier this month, quickly reclaiming Damasak from the terrorists.

According to army source, the militants suffered heavy losses in the push, with an estimated 200 killed in fighting last Sunday.

Boko Haram had held the town since last November, when they killed around 50 people and forced another 3,000 to flee, according to the UN's High Commissioner for Refugees.

The Nigerian military has been struggling for years to stamp out the movement and President Goodluck Jonathan, who is facing an election next weekend, has faced fierce criticism over his government's failure to contain the violence.

Fighting back: A photo released by the Nigerian Army shows soldiers after reclaiming the town of Goniri

The presidential and parliamentary polls were initially due in February but were postponed by the election commission which cited security fears.

Nigeria has claimed major recent gains against the Islamists with the help of coalition partners Cameroon, Chad and Niger, achieving in just over one month what for years it had failed to do on its own.

Two out of three of the worst-hit northeast states -- Yobe and Adamawa -- have been declared 'cleared' while the third, Borno, is expected to be liberated 'soon', the military said this week.