Thad Allen, the official appointed by Barack Obama to lead the federal response to the disaster, gave BP another 24 hours in which to keep the new containment cap on the broken well closed.

But he warned that the US government would reserve the right to reopen the well if worries about seepage intensify.

Allen sent a stiff letter to BP on Sunday night, ordering the oil giant to continue seismic and sonar monitoring around the well to try to get a better picture of what was happening now that the flow of oil had ostensibly stopped.

He said the company had an obligation to inform him of any problems within four hours of any seepage being detected.

“I remain concerned that all potential options to eliminate the discharge of oil be pursued with utmost speed until I can be assured that no additional oil will spill from the Macondo well,” he wrote.

At the heart of the dispute is anxiety about what is happening under the seabed. The government fears oil may be leaking below the surface, and that if left unchecked this process could cause graver problems, including the collapse of the well.

Source:http://www.guardian.co.uk/environment/2010/jul/19/us-bp-capped-oil-well