BP succeeded Sunday in capturing some oil and gas by inserting a mile-long tube into the main Gulf of Mexico leak, but did not say what percentage of the gusher was being contained.

A statement on the latest efforts to control the massive slick off Louisiana and stave off an environmental disaster said a tube had been inserted into the leaking pipe overnight and captured "some amounts of oil and gas."

The process, which saw oil sucked up as if through a straw to a giant drill ship on the surface, comes after US President Barack Obama blasted the companies involved for seeking to shift blame and shirk responsibility.

"The oil was stored on board the Discoverer Enterprise drill ship 5,000 feet above on the water's surface, and natural gas was burned through a flare system on board the ship," the statement said.

BP said it had been forced to halt the effort temporarily when the tube was dislodged from the leaking riser pipe, which connected the Deepwater Horizon to a subsea well until the rig exploded and sank last month, killing 11 workers.

"While this is disappointing, it is not unexpected given the challenging operating environment," the statement said. "Technicians have fully inspected the system and have re-inserted the tool."

BP, under increasing pressure to stem the flow of crude -- estimated to be at least 210,000 gallons a day -- did not say what quantities of oil and gas were being sucked up the tube to the drill ship.

"While not collecting all of the leaking oil, this tool is an important step in reducing the amount of oil being released into Gulf waters," the statement said.

With sheen from the slick now washing ashore in three southern US Gulf states, BP is under massive pressure from officials who have told the firm to clarify what costs it will pay for cleanup.

Fresh analysis of enormous plumes of oil just under the surface of the Gulf meanwhile suggested the spill was far worse than previously estimated.

One was reported to be 10 miles (16 kilometers) long, three miles wide and 300 feet (91 meters) thick.

Researchers from the National Institute for Undersea Science and Technology said the plumes were "perhaps due to the deep injection of dispersants which BP has stated that they are conducting."

Response crews have so far used some 560,000 gallons of the controversial chemical dispersants, spraying them onto surface oil and also directly onto the leak in a bid to break up the oil.

Some environmentalists have suggested that this makes the oil sink but not dissolve completely.

"There's a shocking amount of oil in the deep water, relative to what you see in the surface water," University of Georgia researcher Samantha Joye was quoted as saying by The New York Times.

Oxygen levels have meanwhile dropped 30 percent near the plumes, in an "alarming" trend that is endangering marine life, said Joye, who is on a scientific mission to gather details about the environmental disaster.

On Sunday a large concert in New Orleans was drawing crowds to support Gulf fishermen, whose livelihoods are threatened by the oil spill.

Rock musician Lenny Kravitz was to head a line-up of some 30 groups for the gig to benefit the fishermen who have seen vast swaths of their waters closed by the growing spill.

Obama on Friday accused executives from the three firms most tied to the disaster of creating a "ridiculous spectacle" of finger-pointing and passing the buck.

Two of his top cabinet members have sought to hold BP to public promises it has made to pay all the costs of the containment and clean-up of the spill, which has already run into the hundreds of millions of dollars.

In a letter released Saturday, Homeland Security Secretary Janet Napolitano and Interior Secretary Ken Salazar called on BP chief executive Tony Hayward to provide "immediate public clarification of BP's true intentions."

They said BP's public statements suggested the British energy giant would not seek to have a liability cap applied to claims against it, and would not ask for taxpayer dollars or tap into a liability fund.

Meanwhile, the US Coast Guard told AFP that oil was washing ashore in at least two new locations -- Whiskey Island, Louisiana and Long Beach, Mississippi.

"We sent crews to assess what type of oil, and we determined it's 'soft patties' on Whiskey Island and 'tar balls' on Long Beach," said Petty Officer Erik Swanson.

Oil has also washed ashore on barrier islands in Alabama.