US officials laid out Monday a detailed timeline of how BP plans to permanently plug the Gulf of Mexico oil well, saying the all-important "static kill" would begin in one week's time.

By Saturday or Sunday at the latest, a final 2,000 feet (600 meters) of casing will be inserted into the bottom of the relief well to strengthen it so it can withstand the long-awaited "static kill" intact.

Some 12 hours after the cement has set, engineers will begin the crucial operation to pump mud and cement down through the cap on the damaged well, which finally cut off the flow of crude earlier this month.

"That's an attempt to fill the inside of the well from the top down and then cement to secure it and make it stable," explained Thad Allen, the retired Coast Guard admiral leading the US response to the disaster.

While it is hoped this operation can effectively plug the well, the "static kill" will be followed five days later by a "bottom kill" operation just to make sure.

Engineers will drill through the relief well into the annulus at the bottom of the damaged well. The annulus is the area between the pipe and the outside of the well bore.

The "static kill" can only plug the area inside the pipe, while the "bottom kill" also aims to cement over the annulus to be certain the oil reservoir is permanently sealed.

"So when we enter the well bore of the Macondo well we will first fill the annulus full of mud and then cement it in," said Allen.

"When that cement dries then we will go back and drill through it again and into the pipe.

"We will ascertain at that point whether or not the top kill or static kill have actually killed it or whether we have to do more. That's when we will know absolutely that the well's been killed."

If all goes according to plan, the leaking well could be plugged once and for all during the second week of August.

If upper estimates above four million barrels are confirmed, the disaster that began on April 20 with an explosion on the BP-leased Deepwater Horizon rig, will be the biggest accidental spill ever.