Mr Brown said Britain would meet its promises on aid
Gordon Brown has backed calls for a new international fund to help the world's poorest through the recession.
In a speech to a development conference in London, he said the global financial crisis had hit "the poorest hardest".
World Bank head Robert Zoellick has proposed a fund financed by 0.7% of the money the richest countries are spending on their economic bailouts.
Mr Brown said he would work with the World Bank and other G20 countries to build support for a new fund.
He also said next month's summit of the world's biggest economies would include plans to crack down on tax havens which "siphon off" money from poor countries.
'Stimulus for all'
The two-day conference - which featured contributions from Sir Bob Geldof and senior figures from the World Bank and World Food Programme - looked at ways to ensure the poorest countries were not forgotten in the response to the financial crisis.
Mr Brown said the poorest countries had been worst hit by last year's oil and food price crisis, the worldwide financial crisis and the climate change crisis.
He said: "If we are to move the global economy forward we will need to work together on a fiscal stimulus for all countries and not just some."
He warned that money available to people in developing countries was falling - as money sent home to families was reducing and aid packages were vulnerable to budget cuts.
At the G20 summit in London next month he said the interests of the poorest countries should be "central" to discussions.
"We will work with the World Bank and our G20 partners to build support for a new fund specifically to help the world's poorest through the downturn," he said.
"I want new measures to be targeted at the very poorest, helping to keep girls in school, keep food on the table and keep poverty from the door - so that, when growth returns, people are in a position to contribute to the economy once more."
He added: "While others may be tempted to shy away from their development responsibilities, we in Britain will continue to meet them and we will meet our promises on aid."