Why are Sudan’s warring sides blocking humanitarian aid?

Famine has been declared in Zamzam, a camp sheltering hundreds of thousands of displaced people in Sudan’s North Darfur region.
The crisis is the culmination of 15 months of a war that has claimed tens of thousands of lives and displaced more than 11 million people.
Aid agencies warn that nearly 26 million Sudanese now face acute hunger. That’s a sharp increase since the conflict began in April last year.
Questions are being raised about how this situation was allowed to deteriorate.
Could more have been done to prevent this famine? And what hope is there for the millions still at risk?
Laura Kyle
Kholood Khair – Sudanese political analyst and broadcaster
Amgad Fareid Eltayeb – executive director of the non-partisan think tank Fikra for Studies and Development
William Carter – Sudan country head for the Norwegian Refugee Council