US Interior Secretary Ken Salazar raised expectations Thursday of what he cast as BP's make-or-break attempt to contain the massive Gulf of Mexico oil spill by filling a ruptured well with mud.

As crude oil spread through Louisiana's fragile marshlands a month after a rig blast triggered the spill, BP touted its containment efforts, saying a tube was now siphoning away 3,000 barrels of oil a day from the leak.

BP, which leased the Deepwater Horizon rig that exploded on April 20, hopes to stop the noxious flow with a so-called "dynamic kill" operation, in which heavy drilling fluids would be injected into the well to stem the oil flow, followed by a cement operation to seal it up permanently.

"Our hope is what they call the dynamic kill of this well will happen on Sunday. And that it will be killed. Everything is being done to make sure that happens," Salazar told CNN about the operation also known as a "top kill."

"Our priority is to stop the well from leaking because that's where the cancer is and we need to get that stopped."

But he cautioned that the approach, which will unfold nearly a mile (1,500 meters) below the surface, was "not risk-free," in an interview with ABC television. Speaking on NBC, he urged BP to make sure it was "sparing no resource" to ensure its success.

The firm has also considered combining the "top kill" operation with a "junk shot," where golf balls, rubber tire parts, plastic and other materials would be injected under pressure into a huge valve known as a blowout preventer to clog it up.

The US interior chief, who has come under fire for his agency's lax oversight of the lucrative offshore oil drilling industry, said the government would issue its estimate of the scope of what has grown into one of America's worst oil disasters within days based on satellite imagery.

British energy giant BP estimates that some 5,000 barrels, or 210,000 gallons, a day of crude is spewing from the wreckage of the Deepwater Horizon rig.

But independent experts warn the flow rate could be at least 10 times higher.

"It has been difficult to get a better, more accurate picture of that, because of the very harsh subsea conditions that they're operating on," Salazar said on CNN, noting the figure was needed to inform the public and go after BP for natural resource damages.

"The United States doesn't have anything to hide here. We will have a number that's true and accurate."