There has been a significant increase in the number of children used as human bombs by Boko Haram militants in north-east Nigeria, the United Nations says.

Unicef reports there have been 83 cases so far this year – four times as many as in the whole of last year.

55 were girls under the age of 15 and in one case the bomb was strapped to a baby being carried by a young girl.

Unicef says this tactic is an atrocity causing fear and suspicion of children released by the militants.