The report by two US government-funded famine and food agencies gives the highest toll from Somalia's 2011 famine.
One previous estimate said between 50,000 and 100,000 people died.
A Western official briefed on the report told The Associated Press that it says 260,000 people died, and that half the victims were 5 and under.
Two other international officials briefed on the report confirmed that the toll's report was in the quarter-million range. All three insisted they not be identified because they were not authorized to share the report's contents before it is officially released.