Washington, May 28 (DPA) US President Barack Obama arrived in Louisiana Friday to tour what has become the worst-ever US oil disaster, as energy company BP’s critical top-kill operation to cap the ruptured well in the Gulf of Mexico entered its third day.

Obama’s visit – his second to the region since the April 20 Deepwater Horizon rig explosion – comes amid growing local anger and frustration over the government’s response to the disaster and BP’s inability to cap the oil well.

As many as 540,000 barrels of oil have spewed into the Gulf since April 20, more than the 257,000 barrels during the infamous 1989 Exxon Valdez spill in Alaska. The oil slick has now touched 240 km of US coastline, according to broadcaster CNN.

BP officials insisted the top-kill procedure was proceeding according to plan, though the company warned it would likely be another 48 hours before it was clear whether the complicated procedure was successful.

As part of the operation, heavy mud was pumped into the well through much of Wednesday before engineers took a break to assess results. From Thursday night to Friday morning, BP forced down ‘bridging agents’ such as rubber balls and other solid objects – a variation of the so-called ‘junk shot’ technique.

The pumping of heavy mud was due to resume later Friday, said BP chief executive Tony Hayward. He noted that the operation had already at least temporarily stopped oil and gas coming out of the ruptured well, but pleaded for patience.

‘I know that’s frustrating for everyone. I am probably more frustrated than many,’ he told CNN. ‘I want to get this thing done.’

Hayward has also cautioned that top kill carries a risk of making the leak even larger, so engineers are proceeding with caution. A top kill has never been tried 1.6 km under water.

The halting nature of the process was necessary to allow engineers to measure the pressure in the pipes, BP’s Chief Operating Officer Doug Suttles said Thursday.

‘You stop pumping. If the pressure begins to rise, you pump again. If it doesn’t rise, you have some sign of success,’ Suttles said.

Obama planned to tour Louisiana’s oily beaches and receive a briefing from Coast Guard Admiral Thad Allen, who is leading the federal government’s response to the disaster.

With the growing ecological disaster threatening the livelihoods of local residents, the Obama administration has faced criticism for its handling of the crisis and reliance on BP to cap the ruptured well.

Obama has insisted he carries full responsibility, but that only BP has the technological means to close the leak. Should top-kill not work, BP is also drilling two relief wells that could permanently cut off the oil flow, but the drilling will not be complete until August.

Spain, the Netherlands and the European Union have offered equipment to help the United States clean up the oil, the European Commission said Friday.

The US has so far only accepted help from Mexico and Norway. Obama said Thursday that his administration would consider other offers as needed.