British oil major BP on Thursday successful cut a ruptured oil pile in the Gulf of Mexico, and planned to lower a cap over the undersea gusher.

Remotely operated undersea vehicles work to cut and cap the riser pipe at the site of the Deepwater Horizon oil leak as it continues to spew oil into the Gulf of Mexico in this video image taken from a BP live video feed June 3, 2010. [Xinhua]

"We have just cut the riser pipe off the lower marine riser package," U.S. Coast Guard Admiral Thad Allen, the national incident commander for the Gulf of Mexico oil spill, told a press conference.

A diamond-tipped saw got stuck in the pipe during cutting Wednesday, leading to the use of the shearing device.

A cap will be lowered over the leak shortly, Allen said.

The cap is expected to capture most of the oil leaking from the blown-out wellhead. The broken riser pipe had to be cut off first to allow a snug fit.

This attempt to control the leak is considered risky because slicing away a section of the 20-inch-wide riser could remove kinks in the pipe and temporarily increase the flow of oil by as much as 20 percent.

BP said earlier that the chance of success for this new effort is higher than the failed "top kill" , a two-step operation of pumping heavy fluid into the well to hold back the oil and then sealing the well with cement.

The spill, unleashed by the explosion and sinking of the BP-leased Deepwater Horizon drilling rig late April, has already leaked between 20 million and 44 million gallons of crude, according to government estimates.