The US president has blamed the massive oil spill in the Gulf of Mexico on "a breakdown of responsibility" at energy giant BP as he unveiled a commission to investigate the disaster.
Barack Obama, in his weekly radio and internet address on Saturday, also said offshore oil drilling could only go forward if there were assurances that such an accident would not happen again.
"First and foremost, what led to this disaster was a breakdown of responsibility on the part of BP and perhaps others, including Transocean and Halliburton," Obama said in his toughest remarks yet on companies linked to the spill.
"And we will continue to hold the relevant companies accountable not only for being forthcoming and transparent about the facts surrounding the leak, but for shutting it down, repairing the damage it does, and repaying Americans who've suffered a financial loss," he said.
A month after the well blowout and rig explosion that killed 11 workers, anger is growing along the Gulf Coast as heavy oil washes into delicate coastal wetlands, damaging fishing grounds and wildlife.
In his executive order announcing Bob Graham, a former Democratic senator, and William Reilly, a former Environmental Protection Agency (EPA) chief, as co-chairmen of the commission, Obama made his first reference to the possibility of a criminal investigation.
"The commission shall ensure that it does not interfere with or disrupt any ongoing or anticipated civil or criminal investigation or law enforcement activities or any effort to recover response costs or damages arising out of the Deepwater Horizon explosion, fire and oil spill," the order stated.
The administration is keeping the pressure on BP on many fronts as it strives to show it is being resolute in the face of what many believe is already the worst US oil spill, eclipsing the 1989 Exxon Valdez accident in Alaska.
BP, in charge of the cleanup, said it would be at least Tuesday before engineers can shoot mud into the blown-out well - yet another delay in the effort to stop the oil.
The oil giant made no immediate comment on Obama's remarks, but the company's chief executive, Tony Hayward, said he welcomed the establishment of the commission and pledged to work with its co-chairmen.
"We share the goal of the president and the public to know what happened to cause this accident and what regulatory and industry changes are needed to help prevent something like this from happening again," Hayward said in a statement.
Hayward has said that "the environmental impact of this disaster is likely to have been very, very modest".
Hayward also recently said that "the Gulf of Mexico is a very big ocean - the amount of volume of oil and dispersant we are putting into it is tiny in relation to the total water volume".
|Beachgoers in Louisiana are staying out of the oil polluted water [Reuters]
The EPA expressed frustration on Saturday when it released BP's response to its directive on dispersants instructing the company to evaluate pre-approved dispersants for toxicity and effectiveness.
It accused BP and some of the manufacturers involved of withholding information by invoking business confidentiality.
"EPA continues to strongly urge these companies to voluntarily make this information public so Americans can get a full picture of the potential environmental impact of these alternative dispersants," it said. It did not name the companies.
In its response released by the EPA, BP said Corexit, a dispersant manufactured by Nalco Holding Co that it has been using, was the only one immediately available in sufficient quantities to tackle the spill and "remains the best option for subsea application".
It also said that "within 28 days of application it does not persist in the environment" and asked to discuss the situation with the Coast Guard and the EPA before they issue "directives requiring a change in dispersant products".
Some environmentalists have expressed concerns that the chemicals in dispersants may have a lasting harmful impact.
|BP admits its efforts have not been half as successful as it previously said [AFP]
BP on Friday revised downward an earlier estimate that one of its containment solutions, a 1.6-km-long siphon tube inserted into the larger of two seabed ruptures, was catching 5,000 barrels (795,000 litres) per day of oil.
BP captured 2,200 barrels in the 24 hours to midnight, according to the incident response team, the same figure it had for the previous 24-hour period.
Some scientists have dismissed an original estimate of 5,000 bpd of the total leaking oil - often defended by BP executives - as ridiculously low and say it could be 70,000 barrels or 11 million litres per day, or more.