The former head of the US emergency agency has defended his role in responding to Hurricane Katrina and criticised state and local officials.
Michael Brown strongly denied responsibility for the chaos
Michael Brown, who was fired as head of the Federal Emergency Management Agency (Fema), said Louisiana officials had been reluctant to order evacuations.
He made the statement before a congressional panel investigating shortcomings in the rescue effort.
Mr Brown, who has faced criticism over Katrina, also admitted "mistakes".
Hours later, New Orleans police chief Eddie Compass unexpectedly resigned, after four weeks in which his force has been criticised for its handling of the disaster.
He did not give a reason for his decision, but his announcement came after the New Orleans police department announced it would carry out an investigation into nearly 250 officers who failed to report for duty after the hurricane.
Hurricane Katrina - one of the worst to hit the US - devastated parts of Louisiana and Mississippi on 29 August, causing massive flooding in New Orleans and killing about 1,000 people.
Mr Brown told the congressional panel that Louisiana Governor Kathleen Blanco and New Orleans Mayor Ray Nagin were not co-ordinating their efforts and had been "reticent" in calling mandatory evacuations.
"I very strongly personally regret that I was unable to persuade Governor Blanco and Mayor Nagin to sit down, get over their differences, and work together," he said.
"I just couldn't pull that off."
The former Fema chief, a Republican, denied scoring partisan points - both Ms Blanco and Mr Nagin are Democrats.
He also admitted that he had made "specific mistakes" in dealing with the storm.
He said one was not organising more media briefings.
He added that his "biggest mistake" had been not recognising that Louisiana was "dysfunctional".
Mr Brown also denied that Fema was to blame for the breakdown in law and order in New Orleans.
"Fema is a co-ordinating agency, we are not a law enforcement agency," he said.
Mr Brown was appearing before a panel of the House of Representatives chaired by Tom Davis, a Virginia Republican.
Many Democrats have boycotted the investigation, calling for a independent inquiry.
But one Democrat invited by the panel expressed disbelief at the testimony.
"I find it absolutely stunning that this hearing would start out with you, Mr Brown, laying the blame for Fema's failings at the feet of the governor of Louisiana and the mayor of New Orleans," said William Jefferson, a Louisiana Democrat.
New Orleans was devastated by the impact of Hurricane Katrina
Mr Davis cautioned against assigning blamed too narrowly.
"At the end of the day, I suspect that we'll find that government at all levels failed the people of Louisiana and Mississippi and Alabama and the Gulf Coast," he said.
Following the hurricane, US media and Democratic politicians strongly criticised Mr Brown - saying he lacked disaster expertise.
Before joining Fema in 2001, he held several local government and private posts - including leading the Arabian Horse Association.
Mr Brown resigned on 12 September, saying it was "in the best interest of the agency and best interest of the president".