More than a third of the people in the Sudanese capital, Khartoum, and in the Darfur region are already suffering from acute food deprivation, the agency said.
The number of people entering Ethiopia from Sudan is about 70,000, the International Organisation for Migration (IOM) said.
Earlier on Saturday, U.S. Secretary of State Antony Blinken said representatives of the Sudanese army and the rival paramilitary Rapid Support Forces (RSF) had agreed on a seven-day ceasefire.
But both sides have made it clear they would only discuss a humanitarian truce, not negotiate an end to the war.
A top official said Uganda’s foreign affairs minister is working to evacuate 275 nationals trapped in the deadly military clashes in Sudan.
