The top United Nations aid official in South Sudan is warning of a potential famine if residents aren't able to plant and harvest crops.

Toby Lanzer said Tuesday that following massive fighting that broke out in December, the U.N. is focusing on saving lives, preparing food distribution and "preventing a famine."

More than 800,000 people have been displaced by the fighting. Lanzer said if those displaced can't plant and harvest crops the results could be devastating. The U.N. says 3.2 million people are in need of immediate food aid.

Last week the U.N. said it needs $1.27 billion to tackle the humanitarian crisis. Lanzer stressed that aid must be delivered before the rainy season begins in a couple months, when most of South Sudan becomes inaccessible because of muddy roads.