Officials with BP oil announced a setback Saturday with the company's plan to control an oil spill by lowering a containment dome over the leak.
BP said icelike crystals formed inside the dome and clogged it as it was lowered over the leak more than 1.5 kilometers underwater in the Gulf of Mexico.
Officials said the crystals consisted of flammable hydrate formations. BP said it is working on solutions for the new problem.
As workers scramble to contain the leak, survivors of the deadly explosion said it appeared the blast was caused by a huge bubble of methane gas that traveled up the drilling pipe and caught fire on the surface.
Watch: Video of the Continment Dome Being Lowered
BP workers said a spark from electrical equipment on the drilling rig apparently ignited the flammable gas that traveled up the drill shaft.
That set off a series of major explosions, and the large offshore platform was swept by flames within minutes. Of 126 people aboard the oil rig Deepwater Horizon, 11 men were killed.
BP executives were aboard the rig at the time, celebrating the project's safety record.
An engineering professor at the University of California Berkeley (Robert Bea) who said he obtained transcripts of the workers' interviews after the disaster gave reporters details of what they said.
Since the accident, hundreds of thousands of liters of oil have been pouring out of the shattered well every day. Two days after the rig exploded in flames, the 98-ton structure sank into the Gulf of Mexico, but efforts to plug the oil leak so far have been fruitless.
BP is now working to secure a large containment dome over the gushing well. That tactic has never been tried before at this depth, on a leak of this magnitude, but the dome is seen as the best hope of stopping a major environmental disaster.
If the dome works, it should capture about 85 percent of the leaking oil and funnel it to a tanker on the surface.
U.S. officials have said they will not issue any further offshore drilling permits issued until a federal investigation of the Louisiana spill is completed in about three weeks.
Some information for this report provided by AP and AFP.