Biofuels are coming under increasing attack, having contributed to a 83% rise in global food prices in the last three years, according to the World Bank.

Harsh words are now being spoken. Writing in the Financial Times today, Dominique Strauss-Kahn, head of the International Monetary Fund (IMF), described the push for biofuels as "well-intentioned, yet misguided policies in advanced economies". Last week he said that biofuels "posed a real moral problem" and called for a moratorium on using food crops to power cars, trucks and buses. He said that the vital problem of global warming "has to be balanced with the fact that there are people who are going to starve to death," according to Agence France Presse.

Jean Ziegler, the UN's special rapporteur for the right to food, said last week that "producing biofuels is a crime against humanity."

The issue of rising food prices is dominating a UN trade and development conference in Accra, Ghana. The UN's secretary general Ban Ki-moon told the conference that progress in meeting the UN's millennium development goal of halving world poverty by 2015 could be completely cancelled out by the development.

At a meeting of major world economies on setting climate change targets in Paris last week, EU and Brazilian delegates downplayed the link between biofuels and the world food crisis. Brazil is the world's largest biofuel producer and has been for some years. "There is no real relation of cause and effect between the expansion of the production of biofuels and the raising of food prices. At least it is not happening in Brazil," a spokesperson told AFP.

Meanwhile, EU environment commissioner Stavros Dimas has called for expert advice on how to guarantee that his policies to increase biofuels do not impact on the poor. Dimas told Reuters that the EU is setting sustainability criteria that "must address both environmental and social concerns in order to be able to help us protect the environment and respect social justice".

Sustainability criteria could give a big boost to second generation biofuels made from agricultural by-products that cannot be used for food. At the moment there is a lack of investment in the sector, partly because first generation biofuels are cheaper and easier to produce.

AFP said that another cause of rising food prices is a growing appetite for meat in China and India. It said that on average, it takes more than four kilos (eight pounds) of grain to produce one kilo (two pounds) of pork, and two kilos (four pounds) of grain to yield a kilo (two pounds) of beef. In addition, the rising cost of oil has increased delivery prices, and climate change itself is resulting in lower agricultural yields in some areas. Jean Ziegler himself has criticised EU export subsidies and commodity speculation, as well as biofuels, for causing price increases.