Spill 'is worst US eco-disaster'
The Gulf of Mexico oil spill is the worst environmental disaster the US has faced, a senior official has said.
White House energy adviser Carol Browner also said the US was "prepared for the worst scenario" that the leak might not be stopped before August.
BP is to try a new tactic after its latest failure to halt the leak, but says there is no guarantee of success.
Jane O'Brien reports.