Yaound - A child bomber killed four members of a local self-defence group late on Tuesday in northern Cameroon, an area often targeted by Boko Haram jihadists in their long-running insurgency.The attack in the village of Amchide, near the Nigerian border, was confirmed on Wednesday by a member of the self-defence force who requested anonymity, as well as by a security source in the capital, Yaounde."I was in my sector when I heard a large explosion in another part of the town," the self-defence source said."We saw that a boy had blown himself up in the middle of a group from the security committee," he said.Two people were killed immediately, while two others died from their wounds later, he added.Attacks attributed to Boko Haram fighters have flared in northern Cameroon in recent weeks after months of relative calm, often targeting self-defence groups set up to respond to the jihadist threat. On August 5, a similar attack in the village of Ouro-Kessoum, also near the Nigerian border, killed eight people, following a double suicide attack nearby in July that killed 15.Boko Haram's bloody eight-year armed insurgency, initially focussed on northeast Nigeria, has killed at least 20 000 people and displaced more than 2.6 million. The United Nations on Tuesday warned against the group's surging use of children, mainly girls, as human bombs.Since the beginning of the year, 83 children have been used to carry out bomb attacks in northeast Nigeria, Unicef said, four times as many attacks as in all of 2016.