WASHINGTON: US officials said Wednesday they were highly confident no more oil would leak into the Gulf of Mexico after BP successfully plugged the well, but said there was still a lot more work to do.

We "have reached a static condition in the well that allows us to have high confidence that there will be no oil leaking into the environment," US spill response chief Thad Allen told reporters at a White House briefing.

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

Allen said discussions were ongoing to decide whether to try to permanently seal the reservoir now or wait until later this month when a relief well that he sees as the final solution is completed to allow cementing from the bottom.

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.

"We want to be very, very clear that this does not mean there isn`t more to be done," Browner said. "There remains a lot to be done while sort of the first phase of closing the well may be coming to an end."

BDST: 09:34 HRS, August 05, 2010