The warning came as world leaders arrived in Rome for a global conference to tackle a food crisis that is pushing 100 million people into hunger, provoking food protests and could aggravate violence in war zones.

"The current food crisis amounts to a gross violation of human rights and could fuel a global catastrophe, as many of the world's poorest countries, particularly those forced into import dependency, struggle to feed their people," said Johannesburg-based poverty campaign group ActionAid.

"It is an outrage that poor people are paying for decades of policy mistakes such as the lack of investment in agriculture and the dismantling of support for smallholder farmers," said ActionAid analyst Magdalena Kropiwnicka.

Poor harvests, low stocks and rising demand, especially from India and China, caused huge food price spikes over the last two years, stoking protests, strikes and violence in Africa, Latin America and Asia.

The International Committee of the Red Cross has warned that increased hunger caused by the price spikes will exacerbate conflict in war zones and experts say food riots could worsen if nothing is done.

"Our estimate is that higher food prices are pushing 30 million Africans into poverty," World Bank chief Robert Zoellick told Reuters in Rome, adding that the message he had received from Africans is that they were tired of talk and wanted action.

"We have got a lot of world leaders here, let's try to focus on what we can do in real time to make a difference," said Zoellick, who last week announced $1.2 billion in loans and grants to help poor countries cope with food and fuel costs.

He said immediate action was needed to deliver aid to the countries most at risk, send poor farmers seeds and fertilisers and lift export bans driving up prices.

MUGABE, AHMADINEJAD STEAL LIMELIGHT

Forty-four heads of state and government are expected at the three-day meeting, which kicks off a round of diplomatic talks on poverty, hunger and development in the coming months, including a G8 Summit, a U.N. General Assembly and potentially conclusive talks on new world trade rules.

Japan's Prime Minister Yasuo Fukuda said the summit should issue a "forceful message on medium- to long-term measures such as increasing food production and agriculture productivity."

But the hunger discussions are in danger of being overshadowed by the presence of Zimbabwe's Robert Mugabe and Iran's Mahmoud Ahmadinejad, who both have strained relations with the West.

The European Union has a travel ban on Mugabe, but that does not apply to U.N. meetings.

Britain and Australia called Mugabe's presence at the summit obscene, while the World Jewish Congress said it was deplorable that Ahmadinejad "is allowed to hijack the agenda of this important FAO conference."

Hunger campaigners have targeted the recent rise in bio-fuels -- usually the conversion of food crops into energy -- as one of the main culprits for the price rise and say the summit should declare a ban on arable land being switched to biofuel production.

"To continue the pursuit of biofuels in the face of the credible, impartial and growing opinion that this is exacerbating the food crisis is morally outrageous and utterly indefensible," said Rob Bailey, of hunger campaigners Oxfam.

Under U.S. plans, about a quarter of the U.S. corn crop will be channelled into ethanol production by 2022 as an alternative to crude oil.

U.S. Agriculture Secretary Ed Schafer played down the impact of biofuels on food pricing, saying they only contributed 2-3 percent of overall price rise. Oxfam says the real figure is closer to 30 percent.

Luiz Inacio Lula da Silva, president of Brazil, a pioneer in sugar-cane based biofuels, said he would use the summit to defend biofuels.

"It's up to Brazil, a centre of excellence in ethanol production, to prove that it's fully possible to make ethanol output compatible with the production of food."