President Obama pledges to do whatever it takes to help Americans cope with the biggest oil disaster in US history

US President Barack Obama has pledged to treble the number of emergency crews working to clean up the Louisiana coastline. He made the announcement during a visit to the disaster area. BP says it may not know until Sunday whether its "Top Kill " operation to stop the leak has been successful. According to government figures between 70 and 112 million litres of oil have spilled in to the ocean so far - that's almost three times as much as the 1989 Exxon Valdez disaster.