NEW ORLEANS — BP claimed a key milestone today in a drive to permanently plug its blown-out oil well, upbeat news that dovetailed with a federal report indicating much of the spilled crude has disappeared, though officials cautioned that recovery is far from over.

BP PLC reported mud forced down the well overnight was pushing the crude back down to its source for the first time since the Deepwater Horizon rig exploded off Louisiana April 20, killing 11 workers, rupturing the sea-floor wellhead and causing one of the world's worst oil spills.

Crews still have to determine whether an area between the inner piping and outer casing of the blown-out wellhead is leaking — something they say they can't answer until they drill in from the bottom later this month.

"There's a lot of reasons why there's no 'Mission Accomplished' banner," White House spokesman Robert Gibbs told reporters in Washington.

"There's a lot of work to do," he said. "We're not leaving the area, and more importantly, we're not leaving behind any commitment to clean up the damage that's been done and repair and restore the Gulf."

Still, the plugging is progressing, giving officials high confidence that no more oil will leak into the Gulf, retired Coast Guard Adm. Thad Allen, the government's point man on the spill response, said at a news briefing in Washington.