The United Nations stepped up its campaign for curbs use of crops in making fuels such as ethanol, and pleaded with governments to lay off export curbs and stockpiling, as it appealed for "swift, co-ordinated" action to curtail food price rises causing widespread hunger.

Jose Graziano da Silva, the director-general of the UN's Food and Agriculture Organization (FAO), who last month suggested "an immediate, temporary suspension" of the US mandate on ethanol usage, recruited the heads of  two other agencies for a call on nations to ease off on biofuels consumption.

"We need to review and adjust, where applicable, policies currently in place that encourage alternative uses of grains," Mr da Silva said, in a joint statement with Kanayo Nwanze, the president of the International Fund for Agricultural Development, and  Ertharin Cousin, executive director of the UN World Food Programme.

'Drivers of increased prices'

"Adjusting biofuel mandates when global markets come under pressure and food supplies are endangered has been recommended by a group of international organisations," including the FAO, the International Monetary Fund and the World Trade Organization.

"That recommendation, made to the 2011 G20 summit in Paris, still stands today."

Even in a good year for harvests, "global grain production is barely sufficient to meet growing demands for food, feed and fuel", the statement added, cautioning over food market speculation too.

"Increased diversion of food stock for non-food purposes and increased financial speculation are among the various drivers of increased [food] price levels and volatility."

Ethanol debate

The comments come as the US Environmental Protection Agency has begun a review of the country's so-called renewable fuels standard, or RFS, which this year mandates the use of at least 13.2bn gallons of corn-based ethanol.

US ethanol plants used 5.0bn bushels of corn in the year the end of last month, equivalent to 40% of the domestic harvest, and are expected to increase that proportion to 42% in the new season, according to official data.

Politicians in many US livestock-producing states, and protein groups themselves, have demanded action to curtail use of corn in bioethanol, to free-up supplies for animal feeding.

However, some commentators have warned that the removal of the ethanol mandate would not significantly cut use of the biofuel, with blenders also prizing it for its high octane content.

'Catastrophe' warning

The UN agencies, in Tuesday's joint statement, also cautioned countries to "avoid panic buying and refrain from imposing export restrictions which, while temporarily helping some consumers at home, are generally inefficient and make life difficult for everyone else".

And they stressed, as an "obvious way" of boosting food supplies, growth in agriculture in importing nations, where "there is often huge potential to improve production".

International action was needed urgently on food "make sure that these price shocks do not turn into a catastrophe hurting tens of millions over the coming months.

"In moving to prevent a possible deterioration of the situation, we need to remain vigilant and prepare for the worst in the short run."