New Orleans in aftermath of Katrina   (AP photo)

Congressional leaders say the White House is refusing to cooperate in an investigation of its response to Hurricane Katrina, which devastated the U.S. Gulf coast last year.

Speaking in Washington on Wednesday, Democratic Senator Joseph Lieberman said his staff members were told by federal agency officials the White House has barred them from answering questions pertaining to the probe. Republican Senator Susan Collins also criticized the White House for going too far in restricting information.

A White House spokesman has said the administration is cooperating with the Katrina probe, but added that it wants to protect the confidentiality of presidential advisors.

There has been broad criticism of the response by all levels of government to Hurricane Katrina.

On Monday, documents were released showing that the White House was warned by the Homeland Security Department hours before Katrina hit that the storm's surge could breach levees and leave New Orleans flooded for weeks or months.

A few days after the storm, President Bush said that no one anticipated the breach of the levees.