US President George W Bush says he will lead an investigation into how the Hurricane Katrina disaster was handled.
Little can be done to stop fires in New Orleans' swamped streets
"I'm going to find out over time what went right and what went wrong," he said in reply to criticism that the authorities were too slow to respond.
The US Senate is to hold two inquiries of its own into the disaster which hit the Gulf Coast and New Orleans.
New Orleans' last residents are being urged to leave the swamped city as fires add to the hazards there.
The city's Times-Picayune newspaper has demanded the sacking of top officials at the US Federal Emergency Management Agency (Fema).
One allegation levelled at Fema is that at the height of the crisis it turned away water and diesel because of bureaucracy.
In other developments:
- Environmental experts warn that human sewage and chemical pollution from the flooded city could create a second disaster if they are pumped out untreated into Lake Pontchartrain and the Mississippi
- Two United Nations aid agencies, Unicef and the World Health Organisation, send teams of specialists to Texas and Georgia to help the US federal emergency effort.
'No blame game'
Ex-president Bill Clinton, and his wife, Senator Hillary Clinton, have been among those calling for an inquiry into the handling of Katrina.
How the different levels of government had reacted to Katrina would be examined, Mr Bush said, but he refused to "play the blame game" and said he wanted to focus on the hundreds of thousands of people displaced by the storm.
America, he added, had to be sure it could respond properly to another disaster, whether natural or an attack with weapons of mass destruction.
And he announced that Vice-President Dick Cheney would visit the Gulf Coast region on Thursday to help assess the government's work.
Mr Bush's promise of an investigation falls well short of demands being made by his opponents for a full, independent inquiry, the BBC's Jonathan Beale reports from Washington.
The Senate's homeland security committee and governmental affairs committee are holding their own inquiries, with the latter pointing to "the lack of preparedness and the ineffective initial response to a disaster that had been predicted for years".
America's top soldier, Chairman of the Joint Chiefs of Staff Richard Myers, has denied the military was slow to respond.
"Not only was there no delay, I think we... were pushing support before we were formally asked for it," he said.
'Turning the corner'
Ray Nagin, mayor of New Orleans, has said the relief effort is finally starting to "turn the corner" and the area of the city waterlogged has fallen from 80% to 60%.
He added that at least four fires were burning, and there were fears of oil in the water or gas leaks catching light.
Officials say they have repaired one of the five floodwalls known to have been breached and have started pumping water out into Lake Pontchartrain.
But they said it could take up to three months to finish the job.
Thousands of people are estimated to have been killed in the city.