Aid workers in South Sudan are now fearing for their own safety after six were ambushed and killed over the weekend.
The total number of humanitarian workers killed since the conflict began in 2013, has now risen to almost 80.
About 20 million people in Yemen, South Sudan, Somalia and Nigeria are facing starvation and famine as a result of the humanitarian crisis.
Alex Snary from World Vision, has been in South Sudan recently where he says the crisis is building to the largest humanitarian disaster since 1945.
He says we need to act now to get the food aid in when it's most needed. "The longer the delay, the more people are going to be affected and the greater the casualties at the end of the day."