About 11% of the emergency food aid required in March was provided by donors, leaving a shortfall of 39,000 metric tonnes of cereals, the UN Office of Humanitarian Affairs (OCHA) reported on Tuesday.
While only a quarter of the scheduled food assistance could be distributed last month, the number of needy people is expected to increase from the current 2.4 million to 2.9 million in March and to 3.1 million in April, OCHA said.
Quoting the World Food Programme, OCHA said for the full year, less than a quarter of the 387,500 tonnes of food requested had been made available.
Sporadic fighting between ethnic groups over who would control the Meisso district, about 500km east of the capital Addis Ababa, has left a growing number of people homeless and in need of food, the agency said.
After a costly war with neighbouring Eritrea between 1998 and 2000, Ethiopia - with no seaports and poor communications - is struggling to feed its 67 million people.
Nearly 70,000 people were killed in the border war with Eritrea. About 4000 UN peacekeepers still police a contested 1000km frontier.
The average income is $100 a year, a fifth of the average of sub-Saharan Africa, and 75% of the population live on less than $2 a day, according to UN figures.