The U.S. government is demanding more accountability from BP in the ongoing cleanup of the massive oil spill in the Gulf of Mexico.

The demands come amid growing anger at the oil giant and its handling of the spill, which scientists say is much larger and more serious than BP has admitted.

A sign chastising BP is seen along a highway south of Belle Chasse, La., on Thursday. (Charlie Riedel/Associated Press)The U.S. Environmental Protection Agency on Thursday issued a directive to the oil company to use less toxic chemical dispersants or explain explicitly why it is not doing so.

BP is currently using a bio-degradable, EPA-approved dispersant to isolate the oil slick into separate drops that then evaporate, dissolve, are scooped up or get eaten by microbes.

BP has deployed almost three million litres of dispersant both on the water's surface and 1,500 metres below it at the site of the leak, about 80 kilometres off the coast of Louisiana.

The EPA called that "unprecedented" and said that "much is unknown about the underwater use of dispersants" — a procedure it approved on May 15.

As a result, BP must "identify a less toxic alternative to its current choice — to be used both on the surface and under the water at the source of the oil leak — within 24 hours and to begin using the less toxic dispersant within 72 hours of submitting the alternative," according to the EPA website.

If BP is unable to find an alternative, it will need to explain why it couldn't do so to the EPA and U.S. Coast Guard.

Growing outrage

The EPA's tough stance is the latest example of a growing outrage directed at BP.

On Thursday, BP posted a live video feed of the leak that showed a large plume of oil and gas still spewing into the water despite the stopper-and-tube combination that BP inserted on Sunday to carry some of the crude to the surface.

'I think now we're beginning to understand that we cannot trust BP.' —U.S. Representative Edward J. Markey

The method, never tried before at such depths, captured 800,000 litres at the beginning of the week.

But that amount dropped significantly, to less than 350,000 litres, on Thursday.

"I think now we're beginning to understand that we cannot trust BP," said U.S. Representative Edward J. Markey, a Democrat from Massachusetts. "BP has lost all credibility … It's clear that they have been hiding the actual consequences of this spill."

Doug Suttles, BP's chief operating officer, said Friday his company is "trying to give the data as quick as [it] can."

"I understand that people are very concerned, and they're trying to find what's wrong, and I can understand that," Suttles told CBS's The Early Show.

An undated image from video provided by BP shows oil gushing from the blown well in the Gulf of Mexico, where the Deepwater Horizon rig sank last month. (Senate Environment and Public Works Committee/Associated Press)"They want this thing to come to an end. They want us to be able to clean it up very, very quickly, and we're trying to do these things.

"But at the moment, as you know, what I'm trying to do is figure out how do we get the thing stopped, how do we minimize the impact, and how do we fight this thing at sea."

Ideally, BP will be able to stop the oil flow late Sunday or early Monday with a 'top kill' procedure, Suttles said, referring to a method of clogging the top of the well with various materials and then filling the well itself with heavy mud.

BP is not the only party being blamed for a disaster whose environmental and economic consequences are at this point immeasurable.

State and local officials say the federal government isn't doing enough. President Barack Obama faults the Minerals Management Service, the agency that oversees offshore drilling. Republicans say the Coast Guard and the administration should have done more.

The spill was the result of an explosion on April 20 on the drilling rig Deepwater Horizon, which sank and damaged the pipe leading from the BP oil well, which began leaking hundreds of thousands of litres of oil a day. Eleven workers aboard the rig were killed in the blast.

With files from The Associated Press