The International Organization for Migration warns that many of the millions of people facing famine in three African countries and in Yemen risk starving to death without urgent action to help them.

More than 20 million people reportedly are suffering from severe food shortages in South Sudan, Somalia, Yemen and northeast Nigeria. Somalia's problems are largely due to a severe drought, though conflict also plays a part.

The United Nations says man-made disasters caused by conflict, insecurity, extreme violence and economic degradation are behind the food crises in South Sudan, Yemen and northeast Nigeria.

Famine was declared Feb. 20 in parts of Unity State in South Sudan, and as many as 100,000 people may be at risk, according to IOM spokesman Joel Millman.

FILE - Somalis are seen leaving the Somali capital Mogadishu, due to hunger, for a refugee camp.

"Without access to timely humanitarian aid, famine is likely to spread throughout the country," Millman said. "The number of people facing severe food insecurity is expected to reach 5.5 million by July, the height of the lean season. The current number that we think are facing food insecurity is 4.9 million, so approximately one half million more."

IOM reports the humanitarian situation in Somalia is rapidly deteriorating and the likelihood of famine is increasing. The organization says a growing number of people are fleeing to Ethiopia in search of food and basic services.

As for Yemen, the agency warns the dire food crisis being experienced across the country already has reached famine conditions in some areas. It blames the conflict and worsening conditions for pushing millions of displaced Yemenis into greater danger.

FILE - Children ride on the back of a truck loaded with water jerrycans at a camp for internally displaced people in the Dhanah area of the central province of Marib, Yemen, April 30, 2016.

IOM reports that about 5 million people in northeastern Nigeria are in urgent need of food aid. It says the ongoing Boko Haram insurgency has prevented many people from farming and forced nearly 2 million to flee their homes.

The agency says there is still time to avert a catastrophe and stop famine from spreading throughout these four countries if the international community moves fast.