World Bank President Robert Zoellick has called for reform of biofuel policies in rich countries, urging them to grow more food to feed the hungry.
He was speaking at the G8 summit in Japan, where soaring food and fuel prices are top of the agenda.
The G8 leaders have been holding talks with seven African leaders.
UN chief Ban Ki-moon - also at the summit - urged the group to tackle the "interconnected" challenges of climate change, food prices and development.
Speaking on the sidelines of the summit on Hokkaido island, Mr Zoellick said biofuels - transport fuels made from crops - had made a contribution to food price rises.
He laid particular blame on fuels made from corn and rapeseed produced in the United States and the EU.
"The US and Europe also need to take action to reduce mandates, subsidies and tariffs benefiting grain and oil seed biofuels that take food off the table for millions," he said.
G8 summit: The key issues
Mr Zoellick also urged the G8 to increase food aid and reduce trade barriers on farming products.
The three-day summit is being held at the resort town of Toyako.
As the meeting began, Mr Ban urged G8 leaders to help tackle the food crisis by delivering "the full range of immediate needs, including food assistance as well as seeds, fertiliser and other inputs for this year's planning cycle".
He also told reporters that governments should commit to long-term agricultural investment and lift export restrictions "in particular for humanitarian purposes". His comments came on the same day that the UK announced it would slow its adoption of biofuels amid "increasing questions" about them.
"We need to proceed cautiously until we can be certain that their expanded growth and use maximises the benefits and minimises the risks to our world," said government minister Ruth Kelly.
Aid pledges
Leaders from the G8 nations - Britain, Canada, France, Germany, Italy, Japan, Russia and the United States - are being joined by counterparts from some 15 other countries, including seven African states.
"The best way to help the impoverished around the world is through trade"
The impact on the global economy of price rises and other shocks such as the credit crunch have eclipsed other concerns, correspondents say.
The EU has already been spelling out plans to alleviate the food crisis.
European Commission President Jose Manuel Barroso told reporters that the proposed 1bn euro ($1.6bn; £800m) fund to help poor farmers in developing countries would come from unused EU subsidies.
The G8 leaders are also facing tough questions on aid commitments to Africa.
Campaigners say they are falling short of pledges made at a G8 meeting three years ago to double aid to the continent by 2010.
"They're gradually stepping away from the promises they've made," Oxfam's Max Lawson told AFP news agency.
As well as discussing development issues in Africa, the G8 leaders have been raising Robert Mugabe's controversial re-election in Zimbabwe last month.
US President George W Bush said: "I am extremely disappointed in the elections which I labelled a sham election."
Tanzanian President Jakaya Kikwete, who is also head of the African Union, said the whole continent shared President Bush's concerns but that there was disagreement over what to do about it.
President Kikwete called for a unity government, and said he was optimistic that "as friends at the end of the day we'll come to an understanding".
Protesters have been holding marches in Sapporo, the city closest to the venue, to demand action on global warming, poverty and rising food prices.
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