The United Nations is calling for urgent action to ease the global food crisis that officials say threatens to push millions of people across the globe into poverty and to the brink of starvation.

U.N. Secretary-General Ban Ki-moon Tuesday addressed an international food summit in Rome urging world leaders to boost food output by 50 percent over the next two decades.

The U.N. chief called on governments to administer direct food aid and to supply small farmers in stricken countries with seed and fertilizer before this year's planting seasons. He also urged the elimination of trade and taxation policies that he says distort markets.

In a message, Pope Benedict told delegates that hunger and malnutrition are, in his words, "unacceptable in a world where resources and knowledge" can solve the crisis.

The Rome-based U.N. Food and Agriculture Organization is hosting the three-day summit.

Delegates are slated to discuss the effects of global warming on food availability and the surge in demand for biofuels - made by converting food crops into fuel.

Biofuel opponents say the rising global demand for non-fossil fuels has driven food prices up by as much as 30 percent. That figure has been sharply disputed in Washington, where officials insist biofuels account for only two or three percent of food price increases.

Western delegates have voiced strong opposition to the presence of Zimbabwean President Robert Mugabe at the Rome meeting. Monday, British envoy Douglas Alexander accused the controversial Mr. Mugabe of creating the food crisis in his homeland with "profound mismanagement." Italian activists were also set Tuesday to protest the presence of Iranian President Mahmoud Ahmadinejad.

Some information for this report was provided by AFP, AP and Reuters.