US President George W Bush has said he takes responsibility for government failures in dealing with the effects of Hurricane Katrina.
Anger about the authorities' response has been growing
Speaking at a news conference, he said: "Katrina exposed serious problems in our response capability at all levels of government."
"To the extent that the federal government didn't fully do its job right, I take responsibility."
The president has faced heavy criticism for the reaction to the devastation.
The overall confirmed death toll in the hurricane-affected states is above 600.
Of that total, 423 deaths are confirmed in Louisiana, which includes the worst-hit city of New Orleans.
Meanwhile, the owners of a nursing home where 34 people were found dead after the hurricane have been charged with negligent homicide for each of the deaths.
Salvador A Mangano and his wife, Mable Mangano, surrendered to Louisiana state authorities on Tuesday.
Attorney General Charles Foti told a news conference the two had declined an offer of buses that would have taken their patients to safety.
Officials have said the final number of dead could be much lower than the thousands feared initially.
'What went wrong'
The BBC's Jonathan Beale in Washington says Mr Bush's admission of responsibility does not mean he is prepared to take all the blame but has again pointed to failures throughout government.
"Katrina exposed serious problems in our response capability at all levels of government, and to the extent that the federal government didn't fully do its job right, I take responsibility," Mr Bush said at a news conference.
"I want to know what went right and what went wrong."
Meanwhile, the acting emergencies chief has pledged more help for survivors.
"We're going to get people out of the shelters, we're going to move on and get them the help they need," R David Paulison told reporters.
Mr Paulison took over at the Federal Emergency Management Agency (Fema) after chief Michael Brown stood down on Monday.
Both Mr Bush and Mr Brown have faced severe criticism for the federal government's handling of the disaster.
Mr Bush will address the issue in a major speech to the US people on Thursday, the White House has announced.
Meanwhile the Federal Bureau of Investigation warned people to beware of numerous websites that are claiming to be raising money for Hurricane Katrina relief efforts.
The FBI has so far reviewed more than 2,000 of at least 4,000 sites.
Officials said people should be particularly cautious of sites originating from overseas, which make up around 60% of the total.
A house-by-house search for the dead is continuing in New Orleans and elsewhere. Emergency crews are now reaching outlying areas of Louisiana and neighbouring Mississippi,
The bodies of 45 dead patients have been found in a New Orleans hospital, the biggest discovery of its kind so far.
The BBC's Daniel Lak in New Orleans says the sight of receding waters is starting to tempt a few residents back, despite warnings from the authorities over the health risks.
The city's airport re-opened for commercial flights on Tuesday, in a small sign of progress.
But the first plane to arrive, Northwest Airlines flight 947 from Memphis, Tennessee, had just 30 people on board, AP news agency said.