The World Food Programme (WFP) says it is receiving reports of people dying of starvation in Sudan, where a war has displaced millions of people since last April.
Violence is escalating between the army and a rival paramilitary force as they fight for control of the country.
Security threats and roadblocks have made the work of humanitarian agencies nearly impossible.
Nearly five million people across Sudan now face emergency levels of hunger.
This is twice the number since the start of the conflict, according to the WFP.
The humanitarian body says it has only been able to deliver vital aid to 10% of those in need in areas embroiled in the conflict.
These include the capital, Khartoum, and the western Darfur region, which have endured some of the worst violence.
Earlier this week, the UN's refugee agency said almost eight million people had been force from their homes by the conflict.
Both sides in the conflict - the army and the Rapid Support Forces - have been accused of war crimes.
Attempts to broker peace between the warring factions have so far failed, and in recent weeks fighting has only intensified.
