BP says it is "absolutely responsible" for the oil spilling from a blown-out well in the Gulf of Mexico and is vowing to pay "all necessary and appropriate" costs to clean it up.

"It wasn't our accident, but we are absolutely responsible for the oil, for cleaning it up, and that’s what we intend to do," BP CEO Tony Hayward said Monday morning.

BP CEO Tony Hayward, left, shown at an earlier briefing in Houma, La., on the Gulf oil spill, says his company accepts responsibility for the cleanup costs. (Marc Morrison/Deepwater Horizon Response Unified Command/Associated Press)

The Deepwater Horizon drill rig belonged to Transocean Ltd., he said, referring to the world's largest offshore drilling contractor.

"It was their rig and their equipment that failed, run by their people and their processes, but our responsibility is the oil and the responsibility is ours to clean it up. And that’s what we’re doing."

Guy Cantwell, a Transocean spokesman, responded by reading a statement without elaborating.

"We will await all the facts before drawing conclusions and we will not speculate," he said.

A board investigating the explosion and oil leak plans to hold its first public hearing in about two weeks. The cause of the April 20 explosion, which killed 11 workers, has not been determined.

Three-pronged attack

In a fact sheet posted to the company's website Monday, the British-based BP also said it will pay compensation for "legitimate and objectively verifiable" property damage, personal injury and commercial losses.

President Barack Obama and several state attorneys general have asked BP to provide more details on what that means.

U.S. federal officials shut down fishing from the Mississippi River to the Florida Panhandle on Sunday.

A crew puts down a boom Sunday as part of efforts to contain some of the oil that's been spilling into the Gulf of Mexico since a drill rig exploded April 20. (Gerald Herbert/Associated Press)

Meanwhile, the U.S. government is leading a three-pronged attack on the spill, Secretary of Homeland Security Janet Napolitano said Monday.

The first is to cap the well, which is said to be gushing about 800,000 litres (5,000 barrels) of oil daily from its head 1,500 metres below the water's surface.

The second is to fight the spill on the surface of the sea. The third is to prevent the oil from reaching land and to immediately clean it up if it does, Napolitano said.

Both Napolitano and Hayward defended their organizations' response to the crisis.

"We have been preparing for the worst ever since this came about," Hayward told NBC's Today.

"What BP was estimating and what independent government agencies were also seeing were the same thing," Napolitano told CNN, when asked if the government had put too much faith in BP's response.

"We were already pre-positioning vessels and boom and setting up a command centre, realizing that we were dealing with a situation that was really unknown at that point in time."

Quantifying the size of the spill has proven difficult, although some estimates suggest it measures almost 10,000 square kilometres.

"This spill, at this point in my view, is indeterminate," Admiral Thad Allen, commandant of the U.S. Coast Guard, said Sunday. "That makes it asymmetrical, anomalous and one of the most complex things we've ever dealt with."

Submersibles toil in vain

Efforts to cap the well have so far been fruitless. Eight robotic submersibles continue to try to activate the well's blowout preventer, a valve on the wellhead that experts believe was badly damaged by a pressure surge that may have caused the Deepwater Horizon rig to explode on April 20 and then sink.

A local fisherman waits outside a BP office in Venice, La., on Monday to apply for a contract to work on the oil cleanup. (Carlos Barria/Reuters)

"That is like conducting heart surgery 5,000 feet beneath the sea," Hayward said.

For the first time in industry history, BP is also deploying chemical dispersants at the seabed, which Hayward said "appears to be having a significant impact in limiting the oil that gets to the surface."

It is also constructing a collection device — 67-tonne concrete-and-metal box — that would cover the wellhead and channel the oil gushing out of it to a barge on the water's surface. But that device won't be ready for another seven or eight days, Hayward said.

BP chief operating officer Doug Suttles said drilling of a relief well began Sunday. The aim is to drill down to about 18,000 feet and inject heavy drilling fluids and then cement to cut off the flow of oil to the surface, he said.

Though crews continue to lay booms to contain the spill, high winds have rendered the booms almost completely ineffectual and prevented ships from skimming crude from the surface. Furthermore, teams working to contain the spill have had limited success using airplanes to drop chemical dispersants.

Suttles said oil containment crews encountered seas as high as five metres at the site of the leak, forcing the skimming fleet to return to shore. He said skimming should resume Tuesday, along with the aerial dropping of dispersants.

BP has launched a massive community outreach campaign to co-ordinate the thousands of volunteers who have come forward to help in cleanup operations.

Volunteer activities are focused on clearing existing debris from shorelines, making it easier to clean them should oil wash up, BP said.

Oil pervasive

Even if the oil stays mostly offshore, the consequences could be dire for sea turtles, dolphins and other deepwater marine life — and for microscopic plankton and other tiny organisms near the surface that are a staple of larger animals' diets.

Moby Solangi, director of the Institute for Marine Mammal Studies in Gulfport, Miss., said at least 20 dead sea turtles were found on the state's beaches.

He said it's too soon to say whether oil contamination killed them but it was unusual to have them turning up across such a wide stretch of coast. None of the dead turtles had oil on them, but Solangi said they could have ingested oily fish or breathed in oil on the surface.

The situation could get even worse if the oil gets into the Gulf Stream and flows to the beaches of Florida — and potentially around the state's southern tip and up the Eastern Seaboard. Tourist-magnet beaches and wildlife habitat could be ruined.

If the oil enters what is known as the Loop Current it will likely end up in the Florida Keys and the Gulf Stream, said Nick Shay, a physical oceanographer at the University of Miami Rosenstiel School of Marine and Atmospheric Science. Shay compared the Loop Current to a "conveyer belt" that circles in the Gulf of Mexico, goes through the Florida Keys and up the eastern coast of the U.S.

The oil is expected to enter the Loop Current within a day.

Florida Gov. Charlie Crist has declared a state of emergency for six counties, and Louisiana also has declared a state of emergency.

With files from The Associated Press