Almost a quarter of a million children in parts of Nigeria's Borno state formerly controlled by Boko Haram are suffering from severe malnutrition, the UN children's agency says.

以前由博科圣地所管辖尼日利亚博尔诺州地区，一百万名儿童中近四分之一严重营养不良，联合国儿童基金会说。