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US President Barack Obama has defended his government's handling of the huge oil spill in the Gulf of Mexico.
He unveiled a series of measures, including a continued moratorium on drilling permits for six months.
The move comes after an opinion poll said 60% of Americans were unhappy with the government's response.
BP has resumed pumping heavy mud into the ruptured well after a pause to assess the effect of its "top kill" operation.
The procedure is aimed at stemming the oil flow, from what some experts say is the country's worst-ever spill.
New estimates from a panel of US scientists said at least 12,000 barrels (504,000 gallons) were leaking into the Gulf every day, far exceeding the 1989 Exxon Valdez disaster.
The leak was caused by an explosion on the Deepwater Horizon rig on 20 April, which also killed 11 workers.
Corruption charges
Speaking at the White House, President Obama vowed to hold BP accountable for the "horrific disaster".
He stressed that his administration, and not oil company BP, was in charge.
TOP KILL PROCEDURE Continue reading the main story Drilling mud pumped from surface
Goes into blowout preventer
If pressure and density sufficient, oil and gas flow stops
Well then filled with cement What is a 'top kill'?
But he admitted the government did not have the technology to deal with the damaged oil well nearly a mile (1.6km) below the surface, meaning that Washington must rely on BP to plug the ruptured well.
The president's comments came as questions were increasingly being asked about whether he had been sufficiently engaged in handling the disaster, says the BBC's Adam Brookes in Washington.
In a shake-up of the offshore oil industry, Mr Obama suspended test drilling on 33 rigs in the Gulf of Mexico, as well as halting exploratory deepwater drilling for another six months.
In addition, he cancelled the sale of some offshore leases off the coasts of Alaska and Virginia.
Correspondents say the move marks a shift in policy since March, when President Obama gave the go-ahead to widen the scope for offshore drilling in order to reduce dependency on oil imports.
Hours before Mr Obama spoke, the head of the Minerals Management Service (MMS), which oversees drilling operations, resigned.
Elizabeth Birnbaum and the MMS have come under fire from lawmakers over lax oversight of drilling operations.
The president blasted the "scandalously close relationship" between oil companies and regulators, and said officials granting exploration permits would no longer be responsible as well for ensuring safety.
Also on Thursday, Mr Obama's top spill response official - Coast Guard commander Admiral Thad Allen - approved part of an ambitious plan to build barrier islands to stop oil from coming ashore in Louisiana.
'Worst spill'
The oil leak has already soiled more than 110km (70 miles) of Louisiana's coastline, threatening fragile marshlands and putting the Louisiana fishing industry at risk.
In the first official estimate of the size of the oil leak, US Geological Survey Director Marcia McNutt said government teams estimated the flow ranges from 12,000 barrels (504,000 gallons or 1.9 million litres) to 25,000 barrels per day.
Up to now, BP had estimated the leak at 5,000 barrels (210,000 gallons) per day, while cautioning that figure was unreliable.
If the new estimates are confirmed, it would mean the leak has far eclipsed the previous worst oil spill in US history - the 1989 Exxon Valdez disaster.
Making matters worse, US officials warned the coming hurricane season could be one of the worst on record.
But BP said its latest attempt to stem the flow was making progress.
It would take 24-48 hours before BP engineers could tell whether the "top kill" procedure had worked, company officials said at about 2000 GMT on Thursday.
The procedure, which began on Wednesday, involves pumping heavy drilling fluids into the top of the well to try to halt the oil flow. If it succeeds, cement would then be injected to seal the well.
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A US  official said today that BP's latest effort to plug the Gulf of Mexico oil spill has been successful in slowing the amount of oil leaking from the well.

The official, Admiral Thad Allen, said that the procedure, known as a "top kill" operation, has been able to block some of the leaking oil at the source, the top of the damaged well.  The operation involves pumping material into the well to plug the leak before cement is used to permanently seal the leak.  Allen said the operation has "been able to force mud down and not allow any hydrocarbons to come up."

BP hasn't confirmed the success of the top kill operation, saying only that the "operation is proceeding as we planned it," and that there had been no major incidents thus far.  Although the possibility of failure is still present, experts say that the longer the procedure continues, the less likely it will be that anything goes wrong.

The procedure began yesterday afternoon, after diagnostics on the damaged equipment on the ocean's surface indicated that it could withstand the added pressure of the mud being pumped into the well.  Although engineers involved with the operation wore concerned that the pressure of the mud might not be able to overcome that of the oil, that has thus far not been the case.

Separately, a group of US scientists announced new estimates of how much oil was flowing from the well, ranging from 12,000 to 25,000 barrels a day, far higher than BP's original estimate of 5,000 barrels a day, a figure which BP warned was possibly inaccurate.

In a press conference Thursday afternoon, US president Barack Obama also announced new measures in response to the spill, which include:
*Suspending off-shore test drilling for six months
*Extending the moratorium on issuing drilling permits for an additional six months
*Cancelling the sale of leases for off-shore drilling.
In statements, Obama criticized the "scandalously close relationship" between government officials and oil companies in the past, saying that the Mineral Management Service, which is the agency responsible for monitoring off-shore drilling, had been corrupt for years.