ROME — World leaders at a U.N. summit pledged Thursday to reduce trade barriers and boost agricultural production to combat a food crisis that is spreading hunger and violent unrest across the world.

After three days of wrangling, delegates from about 180 countries approved a declaration resolving to ease the suffering caused by soaring food prices and step up investment in agriculture.

The summit also struck a balance on the contentious issue of biofuels, recognizing that there are both "challenges and opportunities" in using food for fuel.

A few Latin American countries raised strong objections to parts of the declaration.

Cuba was disappointed the document didn't criticize the long-standing U.S. embargo against the Communist-ruled island. Argentina was unhappy it didn't blame farm subsidies in the U.S., European Union and other Western food-producers for a major role in driving up prices.

The declaration called for swift help for farmers in poor countries who need seed and fertilizers in time for the approaching planting season.

"We took the measure of the problem of hunger in the world correctly," said Jacques Diouf, head of the Rome-based U.N. Food and Agriculture Organization, which hosted the summit.

"I think we have an essentially political declaration" of intent to ease hunger, Diouf said.

But it remains to be seen if the words adopted in Rome will translate into changed farm or trade policies at home.

Diouf said that although the gathering wasn't a conference for pledging donations, billions of dollars from countries, regional banks and the World Bank had been promised in recent days.

U.N. Secretary-General Ban Ki-moon had told the summit such measures as import taxes and export restrictions must be minimized to alleviate hunger, and the document called for "reducing trade barriers and market-distorting policies."

U.S. Agriculture Secretary Ed Schafer welcomed the declaration on biofuels, saying the United States remains "firmly committed to the sustainable production and use of biofuels, both domestically and globally."

The biofuel issue was a volatile one at the meeting.

The conference struck a balance on the fuels made from crops such as sugar cane and corn, saying that "in-depth studies" are necessary to ensure that the environmentally friendly energy source does not take food off the table.

Brazil, the United States and other big producers of biofuels disagree on which crops are better-suited to produce the energy source and how much they contribute to driving up food prices.

Cuba's delegation called the document "a step in the process to eradicate hunger," welcoming the declaration despite failing to include language criticizing embargoes. The United States, a huge aid donor, opposes efforts to condemn its embargo on doing business with Cuba.

Monica Robelo Raffone, head of Nicaragua's delegation, contended that the conference had failed to offer solutions or identify the reasons for the price increases.

"It doesn't mention the real causes behind the crisis: the high oil prices, the market speculation, the subsidies. ... It's a step back," she said.

Soaring fuel prices drive up costs of fertilizer and farm vehicle use and transport of food to market. Speculation and increased consumption of meat and dairy goods by populations of China, India and other developing nations is also considered a main factor in the food price hikes.

Zimbabwean President Robert Mugabe's presence and speech at the summit's opening day Tuesday triggered outrage from Western countries, who blame the leader for the economic collapse of a country once considered a regional breadbasket. Some delegations, including the United States, said they wouldn't have dealings with him at the gathering.

The United States on Thursday also condemned what it called Zimbabwe's unjust and outrageous detention of U.S. diplomats and said it would raise the issue at the U.N. Security Council.

Asked about incident at the summit's closing news conference, Diouf said only that all member nations were invited to the summit and "we deal with food and agriculture. We do not get involved in the policies of single countries."