The UN secretary general issued a gloomy warning yesterday that the deepening global food crisis, in which rapidly rising prices have triggered riots and threatened hunger in dozens of countries, could have grave implications for international security, economic growth and social progress.

Ban Ki-moon told a trade and development conference in Accra, Ghana, that the surge in prices of basic foodstuffs like cereals since last year could cancel out progress made towards meeting the UN's Millennium Development Goal of halving world poverty by 2015.

"If not handled properly, this crisis could result in a cascade of others ... and become a multidimensional problem affecting economic growth, social progress and even political security around the world," Ban told the conference.

The World Bank estimates food prices have risen by an average of 83% in the past three years, and warns that at least 100 million people could be tipped into poverty as a result. A range of factors has been blamed, including poor harvests, partly due to climate change, rising oil prices, steep growth in demand from China and India, and the dash to produce biofuels for motoring at the expense of food crops.

"One thing is certain," Ban said. "The world has consumed more than it has produced" over the last three years.

Last week Gordon Brown called for coordinated action by the US and Europe on rising food prices, after discussing the problem with Ban. In his speech yesterday, the UN chief said the ripple effect from food shortages and price hikes risked setting the UN's anti-poverty agenda back at square one. "The global food prices could mean seven lost years ... for the Millennium Development Goals," he said.

The threat of hunger and poverty in developing countries has also sharply increased, and has already resulted in food riots in parts of Asia and Africa.

Ban said several states had attempted to stave off food shortages by barring exports of rice and wheat, or introducing incentives for easier imports of foodstuffs. "This threatens to distort international trade and exacerbate shortages," he said.

The UN's special rapporteur on the right to food, Jean Ziegler, earlier blamed the crisis on biofuels, speculation on commodities markets, and EU export subsidies. "Hunger has not been down to fate for a long time - just as Marx thought," he told the Austrian newspaper Kurier am Sonntag. "This is silent mass murder."

Food riots have broken out in at least a dozen countries, most notably in Egypt, Ivory Coast, Senegal, Yemen and Mexico. Pakistan has reintroduced rationing, while Russia has frozen the price of milk, bread, eggs and cooking oil. Indonesia has increased public food subsidies, while India has banned the export of rice, except the high-quality basmati variety.

Earlier this month, Haiti's parliament dismissed the prime minister, and cut the price of rice, in an attempt to defuse widespread anger at food price hikes that led to days of protests and looting in the capital, Port-au-Prince.

Thousands of garment workers in the Bangladeshi capital, Dhaka, also went on strike this month over spiralling prices. The price of rice, the staple Bangladeshi food, has increased by a third since a devastating cyclone last year. Experts say 30 million of the country's 150 million people could go without daily meals.

The UN food agency has warned that it will need to make "heartbreaking" choices about which countries should receive its emergency aid, unless governments donate more money to buy increasingly expensive food.

In the 30 years to 2005, world food prices fell by around three-quarters in inflation-adjusted terms, according to the Economist food prices index. Since then they have risen by 75%, with much of the increase in the past year. Wheat prices have doubled, while maize, soya and oilseeds are at record highs.