It was difficult to maintain security, she added, in the face of the sea of people trying desperately to get their hands on some food.
Meanwhile on Tuesday, 14 days after the quake, US troops pulled a man alive from under a collapsed building in the capital.
The 31-year-old man had a broken leg and was severely dehydrated, US authorities said.
Outside the wrecked presidential palace, Brazilian UN peacekeeping troops fired tear gas at a frenzied crowd of thousands crowding around a food-handout station.
"They're not violent, just desperate. They just want to eat," Brazilian army Colonel Fernando Soares said. "The problem is there is not enough food for everyone."
Facing persistent complaints by survivors that the huge amounts of aid flown in to Haiti is not reaching them on the ground, US and UN troops, as well as aid workers, have widened and intensified the distribution of food and water.
Al Jazeera's Gabriel Elizondo, also reporting from the capital, said the UN and different aid agencies were trying their best but hundreds of thousands of people were still living in dire conditions.
|Clashes have broken out amid survivors' desperate attempt to get food [Reuters]
"Distribution of food comes with enormous logistical problems and when it arrives at a camp, people rush to it and it gets out of hand," our correspondent said.
Jean-Max Bellerive, the Haitian prime minister, admitted on Tuesday that there were still numerous problems with aid delivery and co-ordination.
Despite some of the food handouts turning unruly, however, the UN said the overall security situation in the city remained stable.
"The vast majority of distributions in Haiti are being carried out in an orderly manner. There are isolated, regrettable incidents but these are the exceptions and not the rule," the World Food Programme said.
The UN food agency said it has delivered nearly 10 million meals to almost 450,000 people since the quake.
Early in the day, a 4.4-magnitude aftershock shook the country, according to the US Geological Survey.
Haiti has been hit by more than 50 aftershocks since a 7.0-magnitude quake hit the country on January 12, each one bringing fresh trauma to survivors.
The aftershocks, lack of basic supplies and government offers of free transportation out of the battered capital have led to about 236,000 people leaving for the countryside since the quake, but the UN said the exodus has slowed to a trickle, with fewer than 1,000 leaving over the past day.
Alex Larsen, the health minister, said one million Haitians had been displaced from their homes in the wrecked capital and the authorities are trying to relocate at least 400,000 survivors from more than 400 makeshift camps to temporary tent villages outside the city.
The government says it has tents for 400,000 to be used in the temporary settlements, but Rene Preval, Haiti's president, has asked the world to send 200,000 more before the rainy season starts in May.