The United Nations says it will need $16.4 billion in 2015 to help 57.5 million of the most vulnerable people in the world.

Last year, the U.N. says it raised $9.4 billion for humanitarian needs — leaving $8.5 billion in unmet needs by the end of 2014. But the U.N. humanitarian appeal a year ago began by asking for $12.9 million to assist 52 million people.

Valerie Amos, the U.N.'s humanitarian chief and emergency coordinator, says more than 80 percent of those in need are in conflict-ridden countries where their lives are devastated by brutality and violence.

She told reporters Monday in Geneva "we are facing needs at an unprecedented level."

U.N. High Commissioner for Refugees Antonio Guterres said the "exponential" rise in needs reflects the growing complexity of crises.