"The response calls for large-scale, high-level action by the global community, focused on emergency and longer-term solutions."

The WFP said this was the biggest challenge in its 45-year history. Riots in poor Asian and African countries have followed steep rises in food prices caused by many factors - dearer fuel, bad weather, rising disposable incomes boosting demand and the conversion of land to grow crops to be turned into biofuel.

"The era of cheap food is over," said Rajat Nag, managing director general of the Asian Development Bank.

Rice from Thailand, the world's top exporter, has more than doubled this year but Nag urged Asian governments not to distort markets with export curbs, and instead use fiscal measures to help the poor.

"We want to temper what we think is a bit of an over-reaction. There is still enough supply," he said.

India and Vietnam have limited exports, hoping to tame prices at home - while goading them higher abroad.

"Banning of exports is no different from hoarding at a national level," Nag said.

The comments from the ADB echoed statements by the International Monetary Fund and the United Nations, urging countries to ensure more funds in the hands of the poor to buy food, instead of resorting to protectionist trade barriers.

Other aid officials have used more dramatic language.

UN Secretary-General Ban Ki-moon has said dearer food risked wiping out progress on cutting poverty and his special rapporteur on the right to food, Jean Ziegler, said rises were leading to "mass murder."

Brown raised further doubts about the wisdom of using crops to help produce fuel, an idea whose recent popularity in the U.S. and Europe has been dented by fears it harms the environment and makes food dearer.

"We need to look closely at the impact on food prices and the environment of different production methods and to ensure we are more selective in our support (for biofuels)," he said.

"If our UK review shows that we need to change our approach, we will also push for change in EU biofuels targets."

The EU's executive Commission on Monday stood by its target of getting 10 percent of road transport fuel from crops and agricultural waste by 2020.

Brown called for more research into higher-yielding crop varieties that can withstand harsh climates and for an agricultural revolution in developing countries.

A global trade deal that opened up markets in rich countries was also needed, he said.

(China Daily via agencies April 23, 2008)