Hours after the British oil giant acknowledged failure in its "top kill" attempt to plug the underwater well, company officials said it could take a week to implement the next bid - placing a cap over the leak.

"Right now we are going to a containment operation," BP Managing Director Bob Dudley told CNN of the latest attempt to deal with the ruptured well nearly a mile (1,600m) under water.

"Because this is being done at 5,000 feet with robots, we're going to take our time, do it extremely carefully. By the end of the week, we should have this in place," Dudley said.

While the "top kill" would have sealed the well using a combination of heavy drilling fluid and eventually cement, the new effort aims only to contain most of the leak, and might temporarily increase the amount of oil gushing into the Gulf of Mexico, officials said.

The well will only be sealed when BP finishes drilling two relief wells, but those are not expected to be ready until August.

In the meantime, hundreds of thousands of gallons of oil spew uncontrolled into the sea each day. At least 20 million gallons are now estimated to have leaked into the ocean since the BP-leased Deepwater Horizon oil rig exploded on April 20 and sank, killing 11 workers.

AFP