A "perfect storm" of drought, conflict and rising costs has increased the ranks of the chronically hungry by millions of people.

This has forced aid workers to find and fund longer-term solutions to the food crisis.

As the world marked World Food Day on Tuesday, the United Nations said the number of chronically hungry people around the globe rises by an average of 4 million each year.

At the same time global fuel prices have soared, pushing up road transport costs and global maritime shipping rates.

The UN's World Food Programme (WFP) says the cost of cereals has risen 50 percent over the past five years, which experts say is due to the world's growing population -- particularly in non-food producing urban areas -- combined with bad harvests and an increased demand for cereal products in previously rice-eating India and China.

Conflict in some of the world's poorest regions has created refugee crises and experts warn climate change may promote more fighting over resources, demolishing coping strategies and pushing already vulnerable families over the edge.

"It is a perfect storm," said WFP Africa spokesman Peter Smerdon. "They all feed into each other."

Worst affected is sub-Saharan Africa, home to 21 of the 36 states worldwide requiring food assistance.

WFP says it is most concerned about Somalia where drought and conflict have coincided to produce what some say is the country's worst humanitarian crisis.

Violence has restricted handouts and fighting between the transitional government, its Ethiopian allies and insurgents has forced thousands to flee Mogadishu to makeshift camps.

The closure of the capital's main market -- a food and job lifeline which has been the scene of repeated fighting and was recently burned -- has also hit supplies and buying power.

In southern Africa, food crises in Zimbabwe and the kingdoms of Lesotho and Swaziland share two causes: drought, which has also hit regional producer South Africa and driven up prices, and AIDS, which has killed farmers and in turn cut output.

Zimbabwe's situation is exacerbated by the seizure of white commercial farmland for landless blacks which has hit output, critics say, and hyperinflation and economic collapse.

West and southern Africa are largely at peace, making access relatively easy but in East and Central Africa's war zones, many of the neediest are out of reach.

New fighting in eastern Democratic Republic of Congo has left WFP unable to reach a third of 300,000 new displaced, while in Ethiopia's Ogaden region government restrictions and a crackdown on rebels are seen blocking aid and trade shipments.

"Populations in these areas are reportedly consuming wild foods and, in the most food-insecure households, slaughtering livestock -- their main source of income -- for consumption," said famine early warning service FEWS NET.

"If trade restrictions continue, these negative coping strategies will lead to destitution."

But while conflict continues to drive food shortages from Sri Lanka to Colombia, hunger is more often caused by deepening poverty.

"If our planet produces enough food to feed its entire population, why do 854 million people still go to sleep on an empty stomach?," the UN Food and Agriculture Organisation Director-General, Jacques Diouf, said in Rome.

Pope Benedict said the world should consider the right to food a universal right for all human beings, without distinction or discrimination.

Increasingly, aid workers say it is time to move beyond handing out food as crises bite. They say simply speaking, longer-term programmes could save money.

Aid group CARE International says its programmes in West Africa's Niger, aimed at reducing poverty and building sustainable agriculture, cost only around $30 a person -- half the price of providing food at the peak of a 2005 food crisis.