A landmine planted by radical group Boko Haram detonated, killing four Chadian soldiers on patrol near Chad’s border with Niger on Saturday, reported security sources.

The soldiers were travelling in a vehicle that rode over the mine at Kaiga Kindji, in the Lake Chad region, which has been plagued by the hardline militants since 2009.

The Nigerian-based Boko Haram wants to create an independently ISIS-styled caliphate in the region and once had occupied an area the size of Belgium.

But a regional offensive led by Nigeria, Chad, Cameroon and Niger – the four countries most affected by Boko Haram – has chased it out of much of that territory.

The group has in response retreated to Nigeria’s Sambisa forest, from where it has fought a paramilitary campaign against civilians and security forces.

Boko Haram is thought to have killed over 15,000 people since the launch of its insurgency seven years ago.
Its rise has strangled economic and farming activity around Lake Chad, leaving tens of thousands hungry.

Nearly half a million children around the lake face “severe acute malnutrition” due to drought and the insurgency by Boko Haram, UNICEF said on Thursday.