Soldiers retreat from Boko Haram stronghold Sambisa Forest

Reports indicate that Nigerian soldiers have retreated from the last known Boko Haram stronghold, Sambisa forest, where they said was booby-trapped after three pro-government vigilantes were killed by a landmine.

According to Reuters, vigilante and a security source both confirmed the pullback from the forest, a day after an offensive aimed at rooting out the insurgents.

"The soldiers have retreated to Bama because of mines. They had been on the road but that made them vulnerable, so they moved to the bush but there are mines planted there (too)," one soldier, who did not want to be named, told Reuters.

The Sambisa forest, a former colonial game reserve, is about 100 km (60 miles) from the village of Chibok, from where Boko Haram abducted more than 200 secondary school girls a year ago.

Intelligence officials believed they were being held in the forest, but U.S. reconnaissance drones failed to locate them.

"Three of our boys were killed by a landmine as we progressed into Sambisa. We've suspended going farther," Muhammad Monguno, a member of a pro-government vigilante, told Reuters

A Chadian military source said a joint military operation involving armies from Niger and Cameroon was expected to begin to encircle the Sambisa forest next week. Chadians will go in from the Cameroonian border where they have been massing troops. 

Over the last six years, Boko Haram have killed thousands and kidnapped hundreds in a battle to establish an Islamic caliphate.