Growing biofuel output would compete with food crops for water, land and capital and thereby increase food prices and "put at risk access to food by the poorest sectors," the FAO said in a report presented at its conference for Latin America and the Caribbean.

It is the latest in a wave of criticism that has questioned the environmental and social benefits of biofuels and put major producers like Brazil on the defensive.

Representatives from oil-rich Venezuela and its regional allies Bolivia, Nicaragua and Cuba harshly criticized biofuels at Monday's conference.

"Without food safety (for the poor) we can't even think about biofuels ... it could create enormous food deficits and social unrest," Gerardo Rojas, Venezuela's vice-minister for rural development, told the FAO meeting.

It is unacceptable for poor countries, which account for only 15 percent of the world's cars, to produce clean fuels for the rich, said Cuban representative Juan Arsenio Quintero.

"We could all save hundreds of millions of dollars and not use a single hectare (of land) with energy efficiency measures," Quintero said.

The criticism is a setback for Brazil, which is trying to spread biofuels production in Latin America and Africa as a tool to end rural poverty by helping small-scale farmers.

Jose Antonio Marcondes Carvalho, Brazil's FAO representative, sought to play down the criticism, saying biofuel production occupied only 1 percent of Brazil's land.

"The real issue is poverty and poor income distribution," Marcondes said, calling on governments to step up social welfare policies.

Mexico called on biofuel critics to present more evidence and Argentina presented its own plans to increase biofuels, citing large potential benefit for its farmers.