BP says its top kill operation to stem the oil leak in the Mexican Gulf will continue for at least another 24 hours.

New official estimates put the leak the worst oil spill in American history.

"Oil is not rising out at the moment," BP's head of communications Andrew Gowers told Today presenter John Humphrys.

"The objective is to pump hard and fast enough, for long enough, to kill the well."

Mr Gowers defended criticisms of BP's speed in dealing with the spill, "the process required careful study and preparation... which is why we are now putting this into practice."

He explained that BP were unable to give a specific timeline for the repairs, "it could be another 24 hours or more, we're can't be completely specific about that because we're still observing an ongoing operation."

When challenged that oil companies needed stronger scrutiny and regulation, Mr Gowers responded, "what has happened in the Gulf of Mexico is a transforming event for the industry and regulation for the industry. Lots of lessons have to be learnt."

Mr Gowers rejected claims that the company had held back on explaining the magnitude of the disaster. "We're not seeking at any point to minimise this. We find it as devastating as much as the residents of the coastal areas, he commented.

Mr Gowers reiterated that BP had taken "full responsibility and are determined to clean up the disaster".