US President Barack Obama was headed to Louisiana on Sunday to survey the oil spill from a damaged off-shore well and the efforts to battle an environmental disaster on the shores of the Gulf of Mexico.
The trip comes amid growing frustration among Gulf state officials about the pace of the response, while the movement of the masses of oil remains unpredictable.
Louisiana Governor Bobby Jindal emphasised in public remarks Saturday evening that it was "day 12" since an April 20 explosion and fire struck the Deepwater Horizon exploratory oil rig, which eventually sank, leaving 11 workers missing and presumed dead.
Federal law makes oil company BP, which operated the rig, responsible for costs and damages, while the effort is coordinated between the company and the US Coast Guard.
"We continue to be concerned about BP's response," Jindal said.
He vowed to voice complaints about the lagging response in his scheduled meeting Sunday with Obama.
BP executives said that drilling a relief well, which is crucial to plans to recap the leaking well, could take 90 days. Authorities estimate that the damaged well is spewing crude oil into the Gulf of Mexico waters at the rate of at least 5,000 barrels a day.
John Brennan, Obama's homeland security advisor, said Saturday evening that the president "wants to make sure that we are moving aggressively and adapting to what is a dynamic situation".
In response to growing criticism of the response to the spill, the administration hastily scheduled Sunday's trip and named Admiral Thad Allen as national incident commander for the spill.
As of Saturday evening, Allen said there was "no reported actual contact with the heavy oil on the beaches in and around Louisiana".
There has been a sheen of oil approaching Louisiana beaches, but the heavy oil seems to be "lingering offshore", he said.
"I think we need to prepare that it will come ashore. We'd obviously like the wind to change and not to happen at all, but the fact of the matter is it's likely to contact shore in Louisiana, Mississippi or Alabama at some point," Allen said.
Three known leaks in the pipe from the wellhead, 1,500 metres deep on the sea floor, threaten a major environmental disaster in the fragile shrimp beds and grassy marshes that line the Mississippi River delta, which provides a lush nursery for birds and marine life.
Louisiana's fishing, shrimp and oyster industries are already grinding to halt, along with sportfishing and other tourist sectors. Major shipping lanes are yet to be affected, the Coast Guard said.
The slick now covers more that 9,000 sq km by some estimates.
Allen said a relief well and related efforts to "stop this thing at the source" was the top priority. BP began positioning equipment and vessels Saturday in preparation for a relief well, but had not started drilling yet.
"We need to attack the oil that is there at sea with all means available - mechanical skimming, dispersant delivery" and burning off the slick, Allen said.
The deployment of booms to stop or slow the advance of oil into sensitive areas, and work to clean up oil that reaches the coast are also key to the response, Allen said.
Windy weather forecast for Sunday was expected to complicate deployment of booms to control the oil and disrupt applications of chemicals to break up the slick. So far, 300 km of booms have been positioned, Allen said.
"We've had pretty good success when the weather has allowed us to deploy dispersants on the oil that's on the surface," Allen said.
The Defense Department contributed two C-130 cargo planes for use in dropping dispersants on large patches of oil.
Allen said that BP has already tested a "promising" scheme to pump dispersants deep toward the wellhead to start breaking up oil as it leaks from the pipe "with the hope that it would disperse the oil there and it would not rise to the surface".
Water samples and other evaluations were being made to see if the dispersant chemicals will harm deep-sea ecology, Allen said.
"It doesn't stop the oil at its source, but it significantly mitigates the amount that will make it to the surface," he said.