International aid workers fear that the deteriorating conditions in Port-au-Prince may put relief efforts in jeopardy, as they try to get food, water and other supplies to survivors of the devastating earthquake in the Haitian capital.

United Nations peacekeepers say that the people who survived Tuesday's 7.0-magnitude quake are growing angrier in the aftermath of the disaster, as they struggle to meet their basic food and water needs. And aid workers may need more security to get their job done.

Warehouses holding the UN World Food Program's food supplies have been looted and the Brazilian military warned aid convoys to bring security with them as they ventured into Port-au-Prince.

"Unfortunately, they're slowly getting more angry and impatient," said David Wimhurst, spokesman for the Brazilian-commanded UN peacekeeping mission. "I fear, we're all aware that the situation is getting more tense as the poorest people who need so much are waiting for deliveries. I think tempers might be frayed."

Aid worker Fevil Dubien said some people were almost fighting over the water he distributed from a truck in a northern Port-au-Prince neighborhood.

Liony Batista, a spokesperson and project manager for Food For the Poor, said he has seen at least one unruly crowd of survivors flock to his agency's headquarters, hoping to obtain some food or water.

"We heard a commotion at the door, knocking at it, trying to get in," said Batista. "'What's going on? Are you giving us some food?' We said, 'Uh-oh.' You never know when people are going over the edge."

The crowd dispersed once they were told food hadn't yet arrived.

"We're not trying to run away from what we do," Batista said. "People looked desperate, people looked hungry, people looked lost."

On the third day after the quake hit, the carnage was still readily apparent in the streets as limbs of the dead protruded from the rubble of downed buildings. Hundreds of bodies were stacked outside the city morgue. Workers were using bulldozers to transport loads of bodies away from the streets.

The exact number of dead is still unknown, though the international Red Cross estimates that between 45,000 and 50,000 people were killed in the disaster.

Foreign governments and agencies have said they will give $400 million worth of aid, including $100 million from the United States. And more than 20 governments have rushed food, water, tents, blankets, water-purification gear, heavy equipment and other materials to Haiti to provide relief.

But their well-intentioned efforts have come up against the limitations of a quake-ravaged Port-au-Prince -- a capital city with a damaged seaport and an airport that doesn't have enough fuel or space for all incoming flights to land. Aid workers who have made it into Haiti have been blocked by debris strewn across inadequate roads and by survivors gathered in the streets.

"I don't think that a word has been invented for what is happening in Haiti," said Batista, the program manager for Food For The Poor. "It is total disaster."

UN engineers have begun clearing some roads and the UN mission's 3,000 international troops and police are working to keep the streets of Port-au-Prince secure, as local Haitian police are "not visible at all," in the aftermath of the quake, said Wimhurst.

Some 5,500 U.S. troops will arrive in Haiti no later than Monday, where they will provide security, said U.S. White House spokesperson Robert Gibbs.

With files from The Associated Press