Gulf oil spill could have impact for 'decades': US official

The massive Gulf of Mexico oil spill could have an "impact for years and possibly decades to come," a top US official said Wednesday, speaking after BP successfully plugged the leaking well.

"We remain concerned about the long term impact," Jane Lubchenco, head of the National Oceanic and Atmospheric Administration, said at a White House briefing.

US spill response chief Thad Allen told reporters at the same briefing that officials were confident that no more oil would leak from the Macondo well, but said there was still a lot more work to do.

Alongside him, President Barack Obama's top energy adviser Carol Browner cautioned that although the so-called "static kill" operation had effectively killed the well, there was still a massive clean-up task ahead.

BP succeeded overnight in plugging its runaway well by ramming in heavy drilling mud for eight hours which drove the oil back down into the reservoir miles beneath the seabed.