Opening a U.N. trade and development conference in Ghana, Ban pledged to use the full force of the world body he heads to tackle the price rises, which threaten to increase hunger and poverty and have already sparked food riots in Asia and Africa.

"I will immediately establish a high-powered task force comprised of eminent experts and leading authorities to address this issue," Ban said, after a group of the world's 49 least developed countries called on Saturday for such a team.

The U.N. head warned the U.N. Conference on Trade and Development (UNCTAD) meeting that huge increases in prices of staple foods such as cereals since last year could erase progress made towards goals set by the U.N. of halving world poverty by 2015.

"The problem of global food prices could mean seven lost years ... for the Millennium Development Goals," he said. "We risk being set back to square one."

Steps by several countries to ban exports of rice and wheat or introduce incentives for food imports also threatened to distort international trade and aggravate shortages, Ban said.

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

World Bank President Robert Zoellick has warned that rising food prices could push at least 100 million people in low-income countries into poverty.

"END AGRICULTURE SUBSIDIES"

West African countries such as Ghana have been among the worst affected by rising food prices caused by factors including poor harvests, record fuel prices, growing demand and tight international supplies. Countries throughout the region, from Mauritania to Cameroon, have witnessed food riots.

Ghanaian President John Kufuor expressed hope the conference would allow developing countries to strengthen economic cooperation and trade, and increase pressure on rich countries to end agricultural subsidies which worsened poverty in Africa.

"Ghana and other African countries are subject to the vagaries of global markets, which leave them with no control over the prices of their own commodities," he said, giving China and India as examples of developing countries that had learned how to benefit from trade and globalisation.

Brazilian President Luiz Inacio Lula da Silva joined both Ban and Kufuor in appealing to all countries to wrap up negotiations for a global trade pact intended to boost the world economy and promote development.

Known as the Doha Round, the negotiations launched in 2001 have stalled and missed past deadlines but momentum has built up in the past two months.

"Achieving success in the Doha Round has become an unavoidable task," Lula said. "Multilateral trade systems can and should contribute to more equitable development."

World Trade Organisation (WTO) Director-General Pascal Lamy, also attending the opening of the April 20 to 25 conference, said a breakthrough in the Doha Round talks could be achieved in the next few weeks.