BP faces criminal probe over oil spill

The confirmation came as BP's stock plummeted and took much of the market down with it, and the US government announced criminal and civil investigations into the spill.

After six weeks of failures to block the well or divert the oil, the latest mission involved using a set of tools akin to a giant slicer and garden shears to break away the broken riser pipe so engineers can then position a cap over the well's opening.

Even if this succeeds, it could temporarily increase the flow of an already massive leak by 20 per cent – at least 100,000 gallons more a day, on top of the estimated 500,000 to one million gallons that have already been lost.

In Florida yesterday, officials confirmed an oil sheen about nine miles from the famous white sands of Pensacola beach. Crews shored up miles of boom and prepared for the mess to make landfall.

Florida would be the fourth state hit. Crude oil has already been reported along barrier islands in Alabama and Mississippi, and it has affected 125 miles of Louisiana coastline.

More fishing waters were closed, too, another setback for one of the region's most important industries. More than one-third of US national waters were off-limits for fishing, along with hundreds of square miles of state-controlled waters.

Attorney General Eric Holder, who visited the Gulf on Tuesday to survey the fragile coastline and meet state and federal prosecutors, would not say who might be targeted in the probes.

"We will closely examine the actions of those involved in the spill. If we find evidence of illegal behaviour, we will be extremely forceful in our response," said Mr Holder.

The US government also stepped up its response to the spill with

President Barack Obama ordering the co-chairmen of an independent commission investigating the spill to thoroughly examine the disaster, "to follow the facts wherever they lead, without fear or favour." The President added that if laws prove insufficient, they would be changed.

If BP's new effort to contain the leak fails, the procedure will have made the biggest oil spill in US history even worse.

"It is an engineer's nightmare," said Ed Overton, a professor of environmental sciences. "They're trying to fit a 21-inch cap over a 20-inch pipe a mile away. That's just horrendously hard to do. It's not like you and I standing on the ground pushing – they're using little robots to do this."

Since the Deepwater Horizon rig exploded on April 20, the leakage has eclipsed the 11 million gallons that leaked from the Exxon Valdez off Alaska in 1989.

BP said that although there is no guarantee the company's latest cut-and-cap effort will work, they remained hopeful.

The UK oil giant has tried and failed repeatedly to halt the flow of the oil, and this attempt – like others – has never been tried before a mile beneath the ocean.

Experts warned it could be even riskier than previous attempts because slicing open the riser could release more oil if there was a kink in the pipe that restricted some of the flow.

BP's best hopes rest with two relief wells but these will probably not be ready until August.

The company has carefully prepared the next phase, knowing that another failure could mean millions more gallons spew into the ocean and lead to even more public pressure.

And they say they have learned valuable lessons from the failure of a bigger version of the containment cap last month that was clogged with ice-like slush.