It is said to be the most impregnable vault on Earth: built out of granite, sealed behind a 22-tonne door, located on a US military base and watched over day and night by army units with tanks, heavy artillery and Apache helicopter gunships at their disposal.

Since its construction in 1937 the treasures locked inside Fort Knox have included the US Declaration of Independence, the Gettysburg Address, three volumes of the Gutenberg Bible and Magna Carta.

For several prominent investors and at least one senior US congressman it is not the security of the facility in Kentucky that is a cause of concern: it is the matter of how much gold remains stored there - and who owns it.

They are worried that no independent auditors appear to have had access to the reported $137 billion (£96 billion) stockpile of brick-shaped gold bars in Fort Knox since the era of President Eisenhower. After the risky trading activities at supposedly safe institutions such as AIG they want to be reassured that the gold reserves are still the exclusive property of the US and have not been used to fund risky transactions.

In other words, they want to be certain that the bullion has not been rendered as valueless as if a real-life Goldfinger had stolen it.

“It has been several decades since the gold in Fort Knox was independently audited or properly accounted for,” said Ron Paul, the Texas Congressman and former Republican presidential candidate, in an e-mail interview with The Times. “The American people deserve to know the truth.”

Mr Paul has so far attracted 21 co-sponsors for a Bill to conduct an independent audit of the Federal Reserve System - including its claims to Fort Knox gold - but an organisation named the Gold Anti-Trust Action Committee (GATA) is taking a different approach.

It has hired the Virginia law firm William J.Olson, PC, to test President Obama's promise to bring “an unprecedented level of openness” to the Government and next month it will file several Freedom of Information requests for a full disclosure of US gold ownership and trading activities.

“We're taking the President at his word,” said Chris Powell, of GATA. “If you go online you can find out how to build a nuclear weapon but you won't find any detailed records on central gold reserves.”

A month after President Nixon resigned over the Watergate affair Congress demanded to inspect the contents of Fort Knox but the trip to Kentucky was dismissed by critics as a photo opportunity. Three years earlier Mr Nixon brought an end to the gold standard when France and Switzerland demanded to redeem their dollar holdings for gold amid the soaring cost of the Vietnam War.

Many gold investors suspect that the US has periodically attempted to flood the market with Fort Knox gold to keep prices low and the dollar high - perhaps through international swap agreements with other central banks - but facts remain scarce and the US Treasury denies that any such meddling has gone on for at least the past decade.

Pressure for more openness is mounting after the collapse of the global banking system and renewed interest in a return to the simpler era of the gold standard - a subject that is likely to be raised at the G20 summit next week. China and Russia are calling for the creation of a new world reserve currency amid fears that the Federal Reserve's quantitative easing policy - essentially printing money - might cause hyperinflation, then collapse.

A spokesman for the US Treasury told The Times that US gold holdings are audited every year by the Department of Treasury's Office of Inspector General. He confirmed that although independent auditors oversee the process they are not given access to the Fort Knox vault.

The website of the US Mint says that the 147.3 million troy ounces of gold in Fort Knox “is held as an asset of the US”. It does not elaborate.

Conspiracy theories

— Area 51, which is part of the Nellis air force base in south Nevada, is at the centre of US conspiracy theories. According to these the base is used to store alien spacecraft, study the corpses of aliens, or develop time travel

— Conspiracy theories suggest that tunnels were built below Denver airport to protect five million people during the coming Armageddon. Some say aliens are housed there

— The Federal Emergency Management Agency (Fema) was established by the US Government in 1979 to co-ordinate a response in the event of a disaster. Since then conspiracy theories have flourished on the theme that Fema concentration camps were being built around the country to incarcerate people and that the Government was soon to declare martial law

— In 1979 an intricate structure made of blue granite appeared on a farm in Elbert County, Georgia. The Georgia Guidestones are inscribed with ten guides written in English, Spanish, Russian, Chinese, Arabic, Hebrew, Hindi and Swahili. An inscription states that its sponsors were “a group of Americans who seek the age of reason”

— Roswell in New Mexico is believed by many to be the site of a UFO crash in 1947, from which an “alien body”, below, was recovered. The US military insists that the debris belonged to an experimental surveillance balloon

Source: Times database

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