AFP - The UN food agency urged greater transparency on commodity markets to prevent sharp spikes in global food prices and deplored the scale of world hunger at a ceremony on Monday marking World Food Day.

"Volatility of food prices challenges the fundamental human right to food," said Jacques Diouf, head of the Food and Agriculture Organisation (FAO), adding:

"There is a need for more transparency in international food markets.

"There is around one seventh of the world population that suffers from hunger, nearly one billion people," said the outgoing FAO chief, who is due to be replaced by Brazilian Jose Graziano da Silva at the end of the year.

Diouf called for world governments to invest an extra $80 billion per year in farming and production to increase reserves by 2050.

Pope Benedict XVI reinforced that message in a statement calling for increased investment in farming to help stabilise production and prices.

"The aim of this day should be an engagement to change behaviour and take decisions in order to ensure that everyone today -- not tomorrow -- has access to the necessary food resources," the pope said in a statement.

"The farming sector should have a sufficient level of investment and of resources to stabilise production and therefore also the market," he added.

The ceremony was also attended by British actor Jeremy Irons and US jazz singer Dee Dee Bridgewater -- two of FAO's goodwill ambassadors.

In its annual report issued last week, FAO warned of high and volatile food prices putting poor families and small farmers at risk.

While some large countries could resist food and economic crises through restrictive trade policies and functioning safety nets, small import-dependent countries, especially in Africa, were vulnerable, FAO said.

It also warned that food prices were likely to remain high and unstable, as demand increases in fast growing economies, populations continue to rise, and growth in biofuel demand puts pressure on the food system.

Global food prices actually fell sharply last month due to production increases in key crop regions, but remain well above last year's levels.

FAO's monthly food price index fell by two percentage points in September compared to August, to 225 points.

That was substantially lower than the record high of 238 points reached in February 2011 but still higher than its September 2010 value of 195 points.

Monday's talks coincide with the start of a week-long meeting of the Committee on World Food Security (CFS) that will address the issue of massive farmland purchases by rich countries in the developing world.

Hopes that the committee would adopt a series of non-binding guidelines for this controversial practice on Monday were disappointed however.

Noel de Luna, chair of the CFS, said discussions on the measures would "be moved towards Friday afternoon pending negotiations."

The issue is commonly referred to as "land grabbing" and non-governmental organisations warn that the practice is threatening the livelihoods of small farmers in poor countries and raising food prices around the world.

"Land grabbing is one of the most blatant and scandalous examples of how the dominant corporate food system is pushing a growing number of farmers and consumers into poverty," the campaign group Via Campesina said.

International aid group Oxfam called for the CFS to fight price volatility by agreeing on scrapping subsidies for turning food into fuel, regulating commodity markets and increasing food reserves in poor countries.

It also called for greater regulation of investments and land governance, as well as a commitment to increased gender equality in agriculture and a massive increase in public investment in small-scale sustainable farming.

"The CFS holds our best hope of ushering in a new era of cooperation that ensures that everybody has enough to eat today and in the future," Barbara Stocking, the chief executive of Oxfam, said in a statement.