Hours after the British oil giant acknowledged failure in its “top kill” attempt to plug the underwater well, company officials said it could take a week to implement the next bid — placing a cap over the leak.

“Right now we are going to a containment operation,” BP Managing Director Bob Dudley told CNN’s “State of the Union” program of the latest attempt to deal with the ruptured well nearly a mile (1,600 meters) under water.

A day after President Barack Obama visited the region for the second time since the oil spill began in April, energy giant BP could offer little but assurances that the bid was ongoing, but that it was too early to judge its success.

“It’s not a nice little black and white operation and they’ve got to take it as it comes,” said Robert Wine, a spokesman for the British firm.

A day after he pledged to take responsibility for stopping and cleaning up the disastrous spill, Obama was in the region for his second visit to assess the situation.

Meanwhile, a US official cited progress in BP’s efforts to plug the leak, but the energy giant warned it would take two days to determine the measure’s success.

“They’ve been able to stabilize the wellhead, they’re pumping mud down it. They’ve stopped the hydrocarbons from coming up,” said Coast Guard chief Thad Allen, who is coordinating the US government’s battle against the oil spill.

He told local radio WWL First News that BP “had some success overnight” but cautioned the British energy giant was “in a period of kind of wait and see right now where they see how the well stabilizes.”

Shortly after winning final approval from US officials for the procedure to go ahead, the British energy giant announced the maneuver dubbed a “top kill” had begun at 1800 GMT.

But after several previous failed attempts to cap the oil, BP boss Tony Hayward has already downplayed hopes of success, cautioning such a procedure has never been tried before at such depth and against such pressure.

BP’s top officer downplayed the likelihood that the desperate effort will succeed in actually sealing the pipe, which is spewing hundreds of thousands of gallons of crude into the Gulf each day.

“If it was on land we would have a very high confidence of success, but… we need to be realistic about the issues around operating in a mile of water,” BP CEO Tony Hayward told reporters on Monday.

Louisiana Governor Bobby Jindal, pleading for sand barriers to be constructed to protect the coast, recounted grim tales of birds unable to fly because their feathers were fused together by oil.

“The Brown Pelican, our state bird. Several months from being removed from the endangered species list,” Jindal implored at a press conference alongside top US government officials in the small town of Galliano.

Initially scheduled to begin on Sunday, BP’s latest attempt to plug a leak in a ruptured pipe 5,000 feet (1,500 meters) below the surface, the “top kill”, is not expected to get under way until Tuesday at the earliest.

As crews used robotic submarines to position equipment to inject heavy drilling fluids into the well and then seal it with cement, the amount of oil being suctioned up by a mile-long insertion tube slowed to 1,360 barrels a day from the previous average of about 2,100.

With the federal government facing accusations of lax supervision of the lucrative offshore oil drilling industry, Obama vowed to hold Washington accountable and warned that the future of the industry hinges on assurances such a disaster would not happen again.

He also sharpened his tone against the three firms involved in the spill — BP, Transocean and Halliburton.

With some of the worst fears of environmental disaster being realized in the marshlands of the Mississippi Delta, BP was also forced to concede it had underestimated the amount of oil leaking into the Gulf of Mexico.

The British energy giant had always maintained only 5,000 barrels — or 210,000 gallons — of crude was gushing each day from a pipe ruptured when its Deepwater Horizon rig exploded one month ago and sank.

The Loop Current has started sweeping leaking crude from the giant slick off Louisiana towards Florida’s popular tourist beaches and fragile coral reefs, threatening a whole new dimension to the unfolding environmental disaster.

Scientists laid out a worst-case scenario in which the oceanic conveyor belt would see the first oil wash up in Florida in as little as six days, before carrying it up the US east coast and even into the Gulf Stream.