Spokesman Jean-Luc Martinage says the organization came up with the estimate based on information from a wide network of volunteers across the quake-stricken capital of Port-au-Prince.
Martinage says it also is a number that government ministers have been using.
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Complete Coverage: Devastation in Haiti
International relief efforts were underway Thursday, but the area in and around Port-au-Prince was proving to be a for aid workers.
U.S. officials say they've from the United States to Haiti at the request of the Haitian government, because there is no room on the ground for more planes and not enough jet fuel for planes to go back.
That comes less than a day after the U.S. military get the airport operating up to full capacity - a critical development for Haitians in desperate need of international relief supplies.
Despite the ongoing recovery efforts, much of Port-au-Prince was still chaotic, with thousands of people filling streets still littered with dead bodies.
On Wednesday, Haitian President Rene Preval said there were likely thousands dead. Soon after, Prime Minister Jean-Max Bellerive said deaths likely numbers in the hundreds of thousands. Then leading Sen. Youri Latortue told The Associated Press that 500,000 could be dead, although he acknowledged that nobody really knows.
Since the earthquake, Preval has maintained his typical low profile, granting only a couple of media interviews and making few public appearances. His own residences were damaged in the quake and the Parliament building collapsed, along with some other 'ministries and departments.
State Department spokesman P.J. Crowley said the U.S. had been in touch with Preval, and added: "We're not taking over Haiti. We are helping to stabilize Haiti, we're helping to provide them lifesaving support."
Earlier Thursday, U.S. President Barack Obama announced that "one of the largest relief efforts in our recent history" is moving toward Haiti, with thousands of troops and a broad array of civilian rescue workers flying or sailing in to aid the stricken country - backed by more than $100 million in relief funds.
To the Haitians, Mr. Obama promised: "You will not be forsaken."
The nascent flow of rescue workers showed some results: A newly arrived search team pulled a U.N. security worker alive from the organization's collapsed headquarters, where about 100 people are still trapped. He stood, held up a fist in celebration, and was helped off to a hospital.
Planes from China, France, Spain and the United States landed at Port-au-Prince's airport, carrying searchers and tons of water, food, medicine and other supplies - with more promised from around the globe for the Western Hemisphere's poorest nation, where the international Red Cross estimated 3 million people - a third of the population - may need emergency relief.
The often-chaotic city was surprisingly calm, despite the devastation, though journalists occasionally heard the sound of isolated gunfire. It was not clear if it was aimed at people. Even in normal times, guards sometimes fire shotguns in the air to keep people away from stores.
There has been widespread looting of collapsed buildings since the earthquake hit, but rarely of undamaged shops, said Matt Marek, Haiti country representative of the American Red Cross.
"There is no other way to get provisions," he told The Associated Press. "Even if you have money, those resources are going to be exhausted in a few days."
Bodies lay in the street, often covered by a white cloth, in the tropical heat. Some people dragged the dust-covered dead along the roads, trying to reach a hospital where they might leave them.
Others tried to carry dead relatives to nearby hills for impromptu burials, prompting Brazil's military - the biggest continent among U.N. peacekeepers - to warn the practice could lead to an epidemic. It said it is asking authorities to create a new cemetery.
The Brazilian military said it also was worried that bodies could be left too long because many Voodoo followers in Haiti do not allow the dead to be touched before all their rituals are concluded.
"This is much worse than a hurricane," said Jimitre Coquillon, a doctor's assistant working at a triage center set up in a hotel parking lot. "There's no water. There's nothing. Thirsty people are going to die."
Aid workers reported confusion over how to cope with the sudden flood of aid from scores of places.
"Donations are coming in to the airport here, but some are coming without notice from very well-meaning groups," said Save the Children spokeswoman Kate Conradt. "There is not yet a system to get it in" to those who need it.
Search and rescue squads from Virginia and Iceland arrived Wednesday and some groups - from Cuba's government and Doctors Without Borders - used physicians already in the country to treat victims immediately after the quake.
Mr. Obama promised Haitians an all-out rescue and humanitarian effort, including the military and civilian emergency teams from across the U.S., adding that America - and the world - "stands with you."
The U.S. Army said a detachment of more than 100 soldiers from the 82nd Airborne Division was heading out from Fort Bragg in North Carolina, looking for locations to set up tents and other essentials in preparation for the arrival of another 800 personnel on Friday.
That's in addition to some 2,200 Marines to be sent, as the military prepares to help with security, search and rescue missions and the delivery of humanitarian supplies. More than a half-dozen U.S. military ships also are expected to help, with the largest, the aircraft carrier USS Carl Vinson, arriving later Thursday.
French Foreign Minister Bernard Kouchner said that 91 injured French nationals were evacuated to the Caribbean island of Martinique in three planes that had delivered aid and medical personnel.
The acrid smell of drywall and ancient dust that filled the air immediately after the quake has faded, giving way to the usual aromas of Port-au-Prince - flowers and mango trees, with a hint of gasoline and urine.
Police officers carried the injured in their pickup trucks. Wisnel Occilus, a 24-year-old student, was wedged between two other survivors in a truck bed headed to a police station. He was in an English class when the quake struck and the building collapsed.
"The professor is dead. Some of the students are dead, too," said Occilus, who suspected he had several broken bones. "Everything hurts."
Other survivors carried injured to hospitals in wheelbarrows and on stretchers fashioned from doors.
Calls to emergency services weren't getting through because systems that connect different phone networks were still not working, said officials from a telecommunications provider in Haiti.
About 3,000 police and international peacekeepers cleared debris, directed traffic and maintained security in the capital. But law enforcement was stretched thin even before the quake and would be ill-equipped to deal with major unrest. The U.N.'s 9,000-member peacekeeping force sent patrols across the capital's streets while securing the airport, port and main buildings.
Port-au-Prince's ruined buildings fell on both the poor and the prominent: The body of Archbishop Joseph Serge Miot, 63, was found in the ruins of his office, said the Rev. Pierre Le Beller of the Saint Jacques Missionary Center in Landivisiau, France.
Haitian Senate President Kelly Bastien was rescued from the collapsed Parliament building and taken to a hospital in the neighboring Dominican Republic. The president of Haiti's Citibank was also among the survivors being treated there, said Rafael Sanchez Espanol, director of the Homs Hospital in Santiago.
The State Department announced one American had died in Haiti, saying that at least 164 U.S. citizens have been evacuated since the quake.
Coast Guard C-130 planes have airlifted 42 American officials and their families and another 72 private citizens to safety, Crowley said.
Another 370 Americans were awaiting flights out, he said. There were about 45,000 Americans living in Haiti at the time of the earthquake.
The International Committee of the Red Cross said it set up a Web site to help Haitians find missing loved ones. Robert Zimmerman, deputy head of the group's tracing unit, said people in Haiti and abroad can use the site to register names of missing relatives.