BP is continuing efforts to plug a massive oil leak in the Gulf of Mexico that has caused the worst oil spill in U.S. history.
The energy giant has resumed pumping heavy drilling fluids into the leaking oil well after suspending the procedure, called a "top kill," for several hours to monitor the results.
The British firm also said it was using another technique, called a junk shot, that involves shooting debris such as rubber and golf balls into the well.
There have been conflicting reports about how the latest effort is going.
Coast Guard commander Admiral Thad Allen, who is overseeing the spill response, said the flow of oil and gas had been stopped -- though the challenge would be whether than can be sustained.
But BP Chief Executive Tony Hayward said that while the effort was "going pretty well according to plan," it would be another two days before he could say if it has worked.
The "top kill" operation has never been tried at 1,500 meters underwater, where the well is located.
If the procedure succeeds, cement will be injected to seal the well.
Meanwhile, it has emerged that far more oil has poured from the well than was previously thought, which would make this the biggest spill in U.S. history.
New estimates released by U.S. government scientists say oil has been gushing out at a rate of between 12,000 to 19,000 barrels, or between 1.9 million and 3.8 million liters, per day.
That's much higher than the 5,000 barrels per day that BP and the U.S. Coast Guard had initially estimated after the well ruptured five weeks ago.
The estimates show that the oil spill is much bigger than the 1989 Exxon Valdez tanker disaster off Alaska in 1989, when 42 million liters of crude were spilled.
The oil leak has already soiled some 160 kilometers of Louisiana coastline, threatening fragile marshlands and putting the state's fishing industry at risk.
Scientists said a thick, 35-kilometer-long plume of oil detected off the BP spill site was nearing an underwater canyon, where it could poison the foodchain for sealife in the waters off Florida.
BP and U.S. officials are also investigating what caused seven crewmembers involved in the clean-up to fall ill.
Demands For Reform
U.S. President Barack Obama, meanwhile, has defended his government's handling of the crisis after critics said it had been too slow to respond.
Obama, who is scheduled to visit the affected area on May 28, vowed to hold BP accountable for the "horrific disaster" and said it was legitimate to question whether BP was "being fully forthcoming about the extent of the damage."
Speaking at the White House, the president unveiled a series of measures, including a continued moratorium on drilling permits.
"We will continue the existing moratorium and suspend the issuance of new permits to drill new deepwater wells for six months," Obama said.
Obama also suspended drilling on 33 exploratory rigs in the Gulf of Mexico and canceled the sale of some offshore leases off the coasts of Alaska and Virginia.
The president also criticized what he said were cozy ties between oil companies and regulators.
"This oil spill has made clear that more reforms are needed. For years there has been a scandalously close relationship between oil companies and the agency that regulates them," Obama said. "That's why we decided to separate the people who permit the drilling from those who regulate and ensure the safety of the drilling."
Hours before Obama spoke, the head of the Minerals Management Service, the government regulator tasked with watching over the oil industry, resigned. Elizabeth Birnbaum and her agency had come under fire from lawmakers over lax oversight of drilling operations.
Obama’s comments also came after an opinion poll said 60 percent of Americans were unhappy with the government's response to the spill.
compiled from agency reports