BP boss Lord Browne visited Prudhoe last week

The investors say they have been let down by failures to repair the pipe in the Prudhoe Bay oilfield, which has been partially closed after a leak.

The closure has drastically cut the field's 400,000 barrels per day output.

A congressional committee is set to examine BP's management of the site - the US's largest oilfield.

The House Energy and Commerce Committee has scheduled a 7 September hearing into the oil giant's corrosion control procedures.

Inaction claims

The legal action from shareholders is seeking unspecified compensation, alleging that senior management "allowed one of BP's prized assets" to decay.

The lawsuit was filed in Manhattan federal court on Monday.

BP spokesman Daren Beaudo said the firm did not comment on legal actions that were pending.

Documents filed with the court accuse BP executives of being aware of the problem of corrosion but alleges they took "no substantial steps to remedy the situation".

BP had considered a total shutdown but now says the oilfield's western half will keep running as pipe repairs and "enhanced surveillance" get under way.

The move will allow BP to supply up to half of the oilfield's usual output, which accounts for 8% of US production.

Global worries

BP has said it will replace 16 miles of pipeline at the site after corrosion was discovered on an oil transit line.

Repairing and substituting corroded pipes could cost around $170m (�89m), BP has said.

It is unclear how this cost will be shared between BP - which owns a quarter of Prudhoe's output - and ConocoPhillips and ExxonMobil, who own the rest.

Prudhoe Bay, which produces around 400,000 barrels per day, is the largest US oilfield.

The threat to this supply comes as conflict in the Middle East and worries over supplies from Nigeria have prompted oil prices to hit record highs recently.

However, on Wednesday morning Brent crude was trading at $73.72 a barrel - some $5 below the record high induced by the Prudhoe Bay leak. US light, sweet crude was at $73.08.