Jacques Diouf, left, and UN chief Ban Ki-moon are both attending
The head of the UN food agency, Jacques Diouf, says he is not satisfied with the final declaration of the UN world food summit in Rome.
Mr Diouf criticised the declaration - which vowed "urgent action" to boost food security - for not including exact targets to reduce hunger.
Aid agency Oxfam also condemned the statement as "un-costed, unfunded and unaccountable".
The UN estimates more than one billion people worldwide are going hungry.
It warns that if more land is not used for food production, 370 million people could face famine by 2050.
The summit's final declaration was issued on the first day of the three-day meeting.
Mr Diouf, head of the UN Food and Agriculture Organisation (FAO), said he was not in the room when negotiators finalised the statement.
But he said he regretted the absence of a deadline for the total eradication of world hunger - referring to the UN Millennium Development Goal deadline of 2015.
"I thought it made sense to set that target, and I thought we would be discussing whether it should be in four years or five years or so on, not that we would be eliminating any target date in the declaration," he said.
"I am not satisfied that some of the concrete proposals I made were not accepted. There was no consensus on this and I regret it."
The BBC's David Loyn in Rome says it was an unusually frank admission from an international civil servant, and reveals frustration that political impetus to increase spending on agriculture may have been lost.
The summit also rejected the UN's call to commit $44bn (£26bn) annually for agricultural development in developing nations.
Matt Grainger, of Oxfam, called the summit a "massive wasted opportunity".
Vatican Radio called the lack of financial targets "disturbing" and Greenpeace described the declaration as "empty rhetoric".
Critics have questioned whether the summit would be effective, as most of the leaders of the world's richest nations are not attending.
Italian Prime Minister Silvio Berlusconi is the only leader from one of the G8 leading industrialised countries to take part.
Opening the summit, UN Secretary-General Ban Ki-moon called for a "single global vision" from world leaders to address the problems of world hunger and pollution.
Pope Benedict XVI also addressed ministers, calling for an end to the "greed" of financial speculation on food prices.
The World Summit on Food Security comes a year after major rises in food prices caused chaos in many developing countries.