David Cameron said people were dying "needlessly" in the drought-hit Horn of Africa as he rebuked other nations for failing to follow the UK's lead in providing assistance.
The Prime Minister said millions of lives could be saved if other countries stepped up aid efforts.
He said he hoped an emergency United Nations food agency summit in Rome would help raise the funds needed to combat the famine in Somalia.
Mr Cameron, who has faced criticism from within his own party for protecting the aid budget at a time of spending cuts, said: "It is, I believe, absolutely right that even in difficult times at home we help those who are facing starvation.
"Britain has led the way with assistance that will help two million people.
"The British people have given another £27 million of their own but the UN still needs more than 300 million dollars more in the next two months in Somalia."
Speaking at a press conference in Downing Street alongside Spanish leader Jose Luis Zapatero, he welcomed Spain's response to the crisis.
But he said: "It is now time for others who have the means in Europe and elsewhere to do more and I hope today's meeting in Rome will produce significant new contributions from other countries.
"We can still save millions of lives. People are starving, people are dying needlessly.
"We have the ability to help, Britain is playing its part, it's now for other countries to do more and to play their part as well."Reuse content