Anger over Mugabe tirade in Rome
Mr Mugabe described the leaders as "unholy men" at the meeting in Rome.
The European Commission responded by saying the tirade justified a travel ban that the European Union imposed on the Zimbabwean leader.
The US accuses Mr Mugabe of starving his people and has said his presence at the food summit is "disheartening".
Mr Mugabe defended his land reforms that have seen thousands of farmers evicted and said rich nations' farm subsidies were "crippling" the poor.
Some delegates to the Rome meeting applauded Mr Mugabe's condemnation of the Western leaders on several occasions during his speech and then at the end.
The Rome conference is being held to mark the 60th anniversary of the UN's Food and Agriculture Organisation (FAO).
Though officially banned from travelling to EU countries, Mr Mugabe is allowed to visit them when on UN business.
European Commission spokesman Amadeu Altafaj expressed regret over Mr Mugabe's "unconstructive" statements.
"What he has been saying in the last days and hours can only confirm the decisions that the European Union took concerning Zimbabwe," Mr Altafaj said.
The US ambassador to the FAO, Tony Hall, said Mr Mugabe, as well as Venezuelan President Hugo Chavez who also criticised Western policy, "chose to politicise an event that was meant to be about feeding the hungry people of the world".
Zimbabwe is struggling to feed an estimated 3.8 million people in the rural areas, and has to import at least 37,000 tons of maize a week.
Mr Mugabe used his speech to lambast President Bush and UK Prime Minister Tony Blair, whose governments have been among his severest critics.
"Must we allow these men, the two unholy men of our millennium, who in the same way as Hitler and Mussolini formed [an] unholy alliance, form an alliance to attack an innocent country?" asked Mr Mugabe, apparently referring to Iraq.
"The voice of Mr Bush and the voice of Mr Blair can't decide who shall rule in Zimbabwe, who shall rule in Africa, who shall rule in Asia, who shall rule in Venezuela, who shall rule in Iran, who shall rule in Iraq," he said.
Mr Mugabe said his land reforms, which enabled the government to seize hundreds of farms owned mostly by white Zimbabweans, had been part of a process to correct colonial injustices.
He blamed agricultural subsidies offered to farm produce from developed countries for crippling "the development of agriculture in developing countries".