UN chief Ban Ki-moon and U.S. Secretary of State Hillary Rodham Clinton led calls Saturday for quick action to ensure global food security as millions suffer from hunger due to the economic crisis and climate change.

Calling chronic hunger and the unrest it can spark "one of the most urgent threats facing our world," Clinton said it's imperative to introduce a comprehensive, co-ordinated approach to the problem, focused at least as much on food production as on emergency aid to prevent famine.

"This is an issue that affects all of us because food security is about economic, environmental and national security for individual homelands and the world," she said.

"There is more than enough food in the world, yet today more than one billion people are hungry," Ban said. "This is unacceptable."

Although food shortages that led to rioting in some developing countries in 2008 have subsided, he said they had highlighted serious deficiencies in the current approach to hunger.

"The food crisis is far from over," Ban said.

"Ever more people are denied the food they need because prices are stubbornly high, because their purchasing power has fallen due to the economic crisis or because rains have failed and reserve stocks of grain have been eaten."

Ahead of a world summit on food security in November, Ban and Clinton said the new efforts must assist small farmers, many of them women, with agricultural expertise to improve crop yields and improve infrastructure to get produce to markets.

In July, the leaders of the Group of Eight leading industrialized democracies pledged the equivalent of about $22 billion Cdn to promote food security. The U.S. will contribute $3.8 billion Cdn to the effort over the next three years and Clinton appealed for other countries to step up.