Palm oil is one of the biofuel crops stirring controversy

The UN's new top adviser on food has urged a freeze on biofuel investment, saying the blind pursuit of the policy is "irresponsible".

Olivier de Schutter also wants curbs on investors whose speculation is, he says, driving food prices higher.

UN officials liken the rise in food prices to a silent tsunami, threatening 100 million of the world's poorest.

The use of food crops for alternative sources of energy like ethanol is one factor behind the price hike.

Mr de Schutter did not go quite as far as his predecessor in the job, Jean Ziegler, the BBC's Laura Trevelyan reports from New York.

Mr Ziegler had condemned biofuels as a "crime against humanity" and called for an immediate ban on their use.

'Predictable' crisis

But the new special rapporteur on the right to food did insist the American and European goals for biofuel production were unrealistic.

I am calling for a freeze on all investment in this sector

Olivier de Schutter

UN special rapporteur on the right to food

"The ambitious goals for biofuel production set by the United States and the European Union are irresponsible," he said in an interview for France's Le Monde newspaper.

"I am calling for a freeze on all investment in this sector."

The biofuel rush was, he argued, a "scandal that only serves the interests of a tiny lobby".

Calling for a special session of the UN Human Rights Council to discuss the food crisis, Mr de Schutter also said he wanted to find ways to limit the impact of speculative investments in food commodities like wheat, which had further driven up prices.

And the rapporteur, a Belgian professor of international law, said it was "unforgivable" that the international community had failed to anticipate the riots sparked last month by soaring food prices.

"Nothing was done to prevent speculation in raw materials, though it was predictable investors would turn to these markets following the stock market slowdown," the UN official said.

"We are paying for 20 years of mistakes."