Oil from BP's out-of-control Gulf of Mexico oil spill could threaten the Mississippi and Alabama coasts this week, U.S. forecasters said on Monday, as public anger surged over the country's worst environmental disaster.

U.S. government and BP officials are warning that the blown-out deepwater well feeding the catastrophic spill may not be shut off until August as the company begins preparations on a new but uncertain attempt to contain the leaking crude.

The London Stock Exchange and Wall Street were closed for holidays on Monday, but BP shares traded in Frankfurt sank 7% to close at around €5.40 on the news of the company's weekend failure to halt the oil leak. BP's stock has lost nearly a quarter of its value since the oil spill started six weeks ago, wiping nearly 29 billion pounds off BP's market value, according to Reuters data.

The disaster, in its 42nd day on Monday, is already the largest oil spill in U.S. history and officials are treating it it as the country's biggest environmental catastrophe. Although Louisiana's wetlands and fishing grounds have been the worst hit so far by the spill, the National Oceanic and Atmospheric Administration said moderate southerly and southwesterly winds this week may start moving oil closer to the Mississippi Delta.

"Model results indicate that oil may move north to threaten the barrier islands off Mississippi and Alabama later in the forecast period," NOAA said in its 72-hour prediction on the expected trajectory of the huge oil slick.

Mississippi and Alabama have escaped lightly so far, with only scattered tar balls and "oil debris" reaching its coasts. But the NOAA forecast was a sober reminder that oil from the unchecked spill, broken up and carried by winds and ocean currents, could threaten a vast area of the U.S. Gulf Coast, including tourism mecca Florida, as well as Cuba and Mexico.

Following the failure this weekend of BP's attempt to plug the leaking mile(1.6 km)-deep well, public anger over the spill and how it occurred is growing, as tens of thousands of Gulf Coast residents face a pollution impact on their livelihoods.

A group calling itself Seize BP, which has already staged anti-BP protests, said on Monday it would organize demonstrations in more than 50 U.S. cities from Thursday to Saturday to protest the damage from the leaking oil. The group demands that BP's assets be immediately seized and held in trust to pay compensation for the spill triggered by the April 20 explosion of the Deepwater Horizon rig.