More than 18.6 million people are experiencing "severe food insecurity," which is 5.6 million more than in the last report in June.
Of those, 2.1 million are experiencing "emergency levels of food insecurity," the report added, with Burkina Faso, Niger and Nigeria being the hardest hit.
Among the factors leading to the crisis are shortages of wheat and fertilizer caused by the Ukraine conflict, regional insecurity and the increasingly serious consequences of climate change, said a report by the UN secretary-general presented to the Security Council.
"The humanitarian situation, especially in the central Sahel, remained dire and was compounded by rising food and energy prices, as well as climate-related disasters, prompted by heavy rainfall, floods and water pollution," the report said.
"Humanitarian access remained limited, depriving vulnerable populations of critical assistance, and exposing humanitarian personnel to increased risks."
Deteriorating security conditions, particularly in Burkina Faso and Mali, have exacerbated the problem, according to the report.