VENICE, Louisiana – Energy giant BP Plc indicated some progress on Monday toward capping the underwater well that ruptured in the Gulf of Mexico almost two weeks ago, pushing a giant oil slick toward the US Gulf Coast.

The British company has been working to plug a leak nearly a mile under the surface of the ocean, under pressure from the US government to try to limit a looming environmental and economic disaster to prized fishing, environmental and recreational areas.

BP said crews in Louisiana have finished building a 74-ton steel and concrete containment dome that the company plans to lower in place over one of the three leaks on the ocean floor.

Drilling also started Sunday night on a relief well that could cap the oil spill on the Gulf floor, the company said. Still, such an operation is expected to take two to three months to complete.

The National Oceanic and Atmospheric Administration projects that the oil slick, which continues to spread over a wider surface area in the warm Gulf waters, will move further east and west by Tuesday, although not necessarily further north toward the coast.

Efforts to prevent the slow-moving mass from washing ashore in parts of four states have been hampered for days by choppy seas and high waves in the Gulf, but forecasts suggest calmer conditions in the next few days.

"The stormy weather is clearing as we speak," Shawn O'Neil, a meteorologist with the National Weather Service in New Orleans, said. "The winds will stay light and variable all the way through Friday. They will have much improved conditions to do what they need to get done."

Miles of booms are being laid along the coast of four states in an effort to contain the movement of oil onto beaches and into key wildlife sanctuaries and breeding grounds.

The Obama administration has kept the focus on BP to pay for and assume responsibility for the oil spill disaster, which started with an explosion April 20 on the Deepwater Horizon rig that killed 11 workers.

For its part, the federal government has come under fire for not responding more quickly to the spreading economic and environmental threat -- criticisms that may have prompted Obama to travel to the affected region on Sunday.

The oil spill, which continues unchecked for now, could ultimately rival the Exxon Valdez disaster from 1989.

That spill was caused when a single, massive oil tanker spewed most of its contents into Alaska's Prince William Sound.

Estimates put the daily flow from the current well leak at 5,000 barrels or more.

Comments by US Attorney General Eric Holder that the Justice Department was involved in the investigation of the incident raised the specter of criminal liability for BP over the spill.

A Justice Department official said it was not a criminal probe at this stage.

Argus Research on Monday downgraded both Transocean and BP Plc to "hold" from "buy" citing negative impact from the Deepwater Horizon spill.

"In many ways, the timing of this incident could not have been worse, as President Obama recently supported the expansion of drilling activity to areas where it was previously prohibited," the brokerage said raising its concern over impact on industry.

In New York, American Depositary Receipts of BP's shares fell 3.7 percent to close at $50.19. Shares Transocean Ltd rose 0.82 percent to 72.91.

Oil prices moved above $86 a barrel as economic optimism lifted Wall Street and concerns the spill could cause short-term disruptions to supplying. So far, major shipping lanes in the Gulf of Mexico have not seen delays.