Nigeria's starving children who fled Boko Haram

Nigeria has been hit by the biggest humanitarian crisis in Africa, with the UN warning that some 100,000 people, mostly children, could die of starvation in the north-east unless they receive urgent aid.

The extent of the crisis has become clearer as the army regains territory from militant Islamist group Boko Haram, which launched an insurgency in 2009 to establish Islamic rule in the region.