Spill response commander won't call 'top kill' successful yet

The man in charge of the response to the Gulf of Mexico oil spill stopped short Thursday of calling the latest effort to stop the leak a "success."

Coast Guard Adm. Thad Allen, who is the national incident commander in response to the spill, stressed that BP's "top kill" procedure to cap its damaged undersea well is continuing.

"It is ongoing," Allen said after repeatedly being asked if the maneuver was a success.

BP had noted signs of success earlier in the day, though it was forced this afternoon to temporarily stop the pumping of heavy drilling mud into the leaking well 5,000 feet below the surface.

"I want to be perfectly clear here: They're pumping the mud into the well bore. As long as the mud is going down, the hydrocarbons are not coming up," Allen explained. The goal is to put enough mud into the well bore to produce zero pressure, which will allow the well to be plugged, he said.

"So, while I said the hydrocarbons have stopped, that does not mean the exercise is over," he added.

The procedure is the most dramatic attempt to end the leak that has spewed millions of gallons into the Gulf of Mexico during the past month and threatens the ecology and economies of Gulf states.