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.
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.
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.
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.