Suspected Boko Haram suicide bombers have killed at least 13 other people in an attack on a market in the northeast Nigerian town of Biu in Borno state, officials say.

Boko Haram's use of child bombers has increased over the last year with one in five suicide attacks now carried out by children, the UN says.

At least 56 people are killed in a double suicide bombing at a camp sheltering people displaced by the Boko Haram insurgency in north-east Nigeria.