The UN is seeking $2bn this year to combat food insecurity in Africa's Sahel region, where 1.2 million people have been forced to flee their homes because of violence.
UN humanitarian chief Valerie Amos announced the appeal in Rome on Monday, saying "more people than ever" were at risk of hunger.
The UN projects 20 million people to be at risk of food insecurity in the Sahel region, with 2.5 million needing "urgent lifesaving food assistance".
According to the UN, five million children younger than five in the region will suffer from malnutrition this year.
At the event in Rome, the UN launched a three-year response plan, to help the Sahel, which it defines as a nine-country region stretching from Chad to Senegal.
"A dramatic increase in the number of food insecure is expected, driven in particular by a deterioration in the food security situation in Northern Nigeria, Northern Cameroon and Senegal. These three countries represent over 40 percent of the overall caseload," the response plan said.
Besides instability in countries like Nigeria and Mali, population growth and high food prices are contributing to the problem.
The three-year plan aims to track and analyse risk and vulnerability to develop humanitarian programmes, respond to warning signals earlier and deliver "integrated life-saving assistance to people affected by emergencies."
"Life-saving naturally continues to be the first priority of the humanitarian community in the Sahel. Special effort will be directed towards a more inter-Cluster response to key vulnerabilities such as food insecurity, malnutrition, epidemics, conflict and displacement and natural disasters," the report said.