People wait to receive food inside the United Nations Mission in South Sudan (UNMISS) Protection of Civilians site (PoC), near Bentiu, northern South Sudan, February 10, 2017. Picture taken February 10, 2017. REUTERS/Siegfried Modola - RTSZG0I

A mother with her child sleep in a bed of the paediatric ward of an hospital in the United Nations Mission in South Sudan (UNMISS) Protection of Civilian site (PoC), outside the capital Juba, South Sudan, January 24, 2017. Picture taken January 24, 2017. REUTERS/Siegfried Modola - RTSZG0V

Women hold their babies as they wait for a medical check-up at a United Nations International Children's Fund (UNICEF) supported mobile health clinic in Nimini village, Unity State, South Sudan February 8, 2017. Picture taken February 8, 2017. REUTERS/Siegfried Modola TPX IMAGES OF THE DAY - RTSZN4N

A man collects sacks of food from a dry river bed after a United Nations World Food Programme (WFP) airdrop close to Rubkuai village in Unity State, northern South Sudan, February 18, 2017. Picture taken February 18, 2017. REUTERS/Siegfried Modola - RTSZG0J

A United Nations World Food Programme (WFP) plane releases sacks of food during an airdrop close to Rubkuai village in Unity State, northern South Sudan, February 18, 2017. Picture taken February 18, 2017. REUTERS/Siegfried Modola - RTSZFZZ

Women carry boxes of nutritional food delivered by the United Nations World Food Programme (UN WFP), in Rubkuai village, Unity State, South Sudan February 16, 2017. Picture taken February 16, 2017.

A mother feeds her child with a peanut-based paste for treatment of severe acute malnutrition in a UNICEF supported hospital in the capital Juba, South Sudan, January 25, 2017. Picture taken January 25, 2017. REUTERS/Siegfried Modola TPX IMAGES OF THE DAY - RTSZFZX

People walk by inside the United Nations Mission in South Sudan (UNMISS) Protection of Civilians site (PoC), near Bentiu, northern South Sudan, February 9, 2017. Picture taken February 9, 2017. REUTERS/Siegfried Modola - RTSZG0T

People move away from as a United Nations World Food Programme (WFP) helicopter lands in Rubkuai village, Unity State, northern South Sudan, February 17, 2017. Picture taken February 17, 2017. REUTERS/Siegfried Modola - RTSZG0C

A woman cooks a meal in the town of Pibor, Boma state, east of South Sudan, February 2, 2017. Picture taken February 2, 2017. REUTERS/Siegfried Modola - RTSZG0W

A man collects sacks of food from a dry river bed after a United Nations World Food Programme (WFP) airdrop close to Rubkuai village in Unity State, northern South Sudan, February 18, 2017. Picture taken February 18, 2017. REUTERS/Siegfried Modola - RTSZG0J

Women wait in line during a UNICEF supported mobile health clinic in the village of Rubkuai, Unity State, South Sudan, February 16, 2017. Picture taken February 16, 2017. REUTERS/Siegfried Modola TPX IMAGES OF THE DAY - RTSZHLU

A boy moves away as a United Nations World Food Programme (WFP) helicopter lands in Rubkuai village, Unity State, northern South Sudan, February 18, 2017. Picture taken February 18, 2017. REUTERS/Siegfried Modola TPX IMAGES OF THE DAY - RTSZG00

Women carry sacks of food in Nimini village, Unity State, northern South Sudan, February 8, 2017. Picture taken on February 8, 2017. REUTERS/Siegfried Modola TPX IMAGES OF THE DAY - RTSZHLT