The U.N. Office for the Coordination of Humanitarian Affairs said a food and nutrition crisis in the region is deteriorating rapidly.
The aftermath of the 2011 civil war in Libya, meanwhile, created security complications in the region as armed fighters and criminal gangs returned home with large quantities of weapons.
U.N. High Commissioner for Refugees Antonio Guterres said international support was a critical need.
"The Sahel represents a deadly combination of drought and displacement by conflict," he said in a statement. "This is not only a dramatic humanitarian problem but it has become a threat to global peace and security."
His agency is working from Burkina Faso, Mauritania and Niger to help the thousands of displaced refugees cope with the crisis. Conflict in the region has spread from Mali to Guinea-Bissau.
The United Nations estimates more than 15 million people are facing food shortages and malnutrition due to a lingering drought. More than 200,000 children died of malnutrition last year and more than 1 million children are threatened.
"Time is not on our side," Ertharin Cousin, executive director of the World Food Program, said in a statement.