Obama ramps up pressure on BP for Gulf of Mexico oil disaster

US president Barack Obama on Saturday blamed the massive Gulf of Mexico oil spill on "a breakdown of responsibility" at energy giant BP plc as he officially unveiled a commission to investigate the disaster.

Obama, in his weekly television and internet address, also said offshore oil drilling could only go forward if there were assurances that such accidents would not happen again.

While ramping up pressure on firms linked to the still uncapped spill — BP, Halliburton, and Transocean Ltd — Obama said he would also hold Washington accountable for mending its ways.

With the political stakes growing, Obama had his toughest words yet for companies linked to the spill.

"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," he said.

"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 have suffered a financial loss," he said.

A month after the well blowout and rig explosion that killed 11 workers, sheets of rust-coloured heavy oil are starting to clog fragile marshlands on the fringes of the Mississippi delta,  damaging fishing grounds and wildlife.

The spill has raised major questions about Obama's earlier proposal to expand offshore drilling as part of strategy to win Republican support for climate change legislation.

In the Republicans' weekly address, Louisiana senator David Vitter criticised the Democrats in Congress for rushing to hold hearings on the spill "instead of devoting full attention to stopping the immediate problem".

Vitter also said the spill should not be used to justify a clampdown on offshore drilling, saying "ending all domestic energy production offshore would only make us that much more dependent" on foreign sources of oil.

In his executive order announcing that former Democratic senator Bob Graham and and former Environmental Protection Agency chief William Reilly would co-chair the commission, Obama made his first reference to the possibility of a separate criminal probe.

"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.

Attorney general Eric Holder said on May 3 that the justice department was part of the investigation into the spill, though a US official at the time said it was not a criminal inquiry.

Mark Salt, a BP spokesperson, said the company had no immediate comment about Obama singling out anyone for possible blame in the accident.

"We're not going comment on what happened," Salt said. "We're going to wait until the investigation has taken its due course."

US lawmakers and scientists have accused BP of trying to conceal what many believe is already the worst US oil spill, eclipsing the 1989 Exxon Valdez accident in Alaska. It represents a potential environmental and economic catastrophe for the US Gulf coast.

"To me from the very beginning with BP it was nothing but public relations," said Roger Halphen, a South Louisiana schoolteacher who has worked both in the oil industry and as a commercial fisherman.

"It's just a disaster. Everybody was sleeping on this and all of a sudden here it is," he said of oil washing up on the coast.

BP's battered reputation has been reflected in its share price, which lost more than 4% in London on Friday, extending recent sharp losses.

London-based BP has said its engineers are working with federal scientists to determine the size of the leak, even as they fought to control the gushing crude with uncertain solutions.

BP revised downward on Friday an earlier estimate that one of its containment solutions — a 1 mile (1.6km) long siphon tube inserted into the larger of two seabed leaks — was capturing 5,000 barrels (210,000 gallons or 795,000 litres) of oil per diem.

The company's next planned step is a 'top kill' — pumping heavy fluids and then cement into the gushing well to plug it.

"The riser insertion tool continues to operate and collect oil and we are still progressing [with] the top kill, which will be deployed on Tuesday at the earliest," Toby Odone, a BP spokesperson, said on Saturday.

Many scientists dismiss an original 5,000 bpd estimate of the total leaking oil — often defended by BP executives — as ridiculously low and say it could be 70,000 barrels (2.9 million gallons or 11 million litres) a day or more.

A federal panel will release its estimate of the actual flow rate as early as next week, a coast guard officer said.

Scientists fear parts of the huge fragmented surface slick will be sucked to the Florida Keys and Cuba by ocean currents.