After the discovery of "unexpectedly severe" corrosion and oil spillage on a pipeline in Alaska, British Petroleum officials announced they would temporarily close the Prudhoe Bay field. The company said it was unable to estimate how long production would be disrupted.

Oil drilling at the Prudhoe Bay field had already caused major environmental damage and should be closed permanently, according to Hans-Josef Fell, the German Green party's energy spokesman, who added that the Alaskan wilderness should be protected, rather than "polluted with oil."

"When we dig out the oil we dig out the carbon into the atmosphere and climate protection is very important," Fell said. "If we go on with this oilfield, we have all problems of energy security of supply because Prudhoe Bay is already in decline, and in the next years we will get less and less oil from this field."

No estimate on when oilfield could reopen

The Alaskan oilfield is the largest in the United States and produces about 400,000 barrels of oil per day, accounting for about 8 percent of total US oil production. BP began the shutdown late on Sunday, after discovering an oil transit line had corroded, causing the oil leak. An estimated four to five barrels of crude oil were lost and had begun to contaminate the surrounding ice.

BP America chairman Bob Malone said the plant would remain closed until the company and government regulators were satisfied the pipelines were safe and posed no threat to the environment.

The damage in Alaska is a further blow to the Prudhoe Bay plant, after around 1 million liters (264,172 gallons) leaked from a pipeline in March 2006 and another blow to BP's US operations, which also suffered an explosion that killed 15 people at a Texas plant in March 2005.

Investment in alternative energy

Fell said he believes BP should invest in new forms of energy rather than repairing the neglected pipelines.

"It would be better to make new investments in bio-fuels or other renewable energy so we can have a lot of energy all over the next decades and not only for some years from oil from Prudhoe Bay," he said.

To avoid future energy shortfalls, he suggested BP live up to the company's slogan "Beyond Petroleum."

"BP already has some investments in renewable energy, but it is not enough," he said. "BP has huge amounts of profits and should give to renewable energy so we will have enough to fulfill our energy supply."

Oil prices drop from all-time high

With oil supplies at a premium, partially caused by instability in the Middle East, analysts said the closure represents a sizeable loss to the world market.

Following the shutdown, crude oil prices for jumped by more than $2 (1.56 euros) per barrel to reach a high of $78.64 in London before dropping later to $77.79 on Tuesday. The increase has come at a time when oil prices are already at record highs.