The report, which examines the fate of gold looted by the Nazis during the war, said four countries - Portugal, Spain, Sweden and Turkey - were as crucial to the Nazi war effort as neighbouring Switzerland.

BBC correspondent Bill Turnbull in Washington on the role of the neutral countries (1'34")

It states the "neutrals" were paid for crucial commodities through the Swiss National Bank with gold that Hitler's troops had looted from other banks, and valuables stolen from Holocaust victims.

The report was the second by Undersecretary of State Stuart Eizenstat who has headed US efforts to determine the fate of Nazi gold.

His first report, produced in May 1997, detailed how Switzerland assisted Hitler and then frustrated efforts to recover the Nazis' stolen gold after Germany's surrender.

The neutral's 'critical role'

The latest report describes Switzerland as a "financial facilitator", turning gold looted from Holocaust victims and conquered countries, into Swiss francs.

Nazi gold, the means to make weapons

But it states that Portugal, Spain, Sweden and Turkey "played an equally critical role in sustaining the war effort" by providing Nazi Germany with minerals essential for making weapons.

"You couldn't have had one without the other," Mr Eizenstat said.

"Clearly if the gold hadn't been transferred into Swiss francs, then they (the Nazis) wouldn't have had a medium of exchange. On the other hand, if the other (neutral countries) hadn't supplied the raw materials, then the gold would not have been terribly useful."

Billions in trade

According to the report:

• About $300m in looted Nazi gold, worth $2.6bn today, was used to pay Portugal, Sweden, Turkey and Spain for war material. Three-quarters of the amount was transferred through the Swiss National Bank.
• Portugal and Spain provided Germany with almost 100% of its wartime supply of wolfram - the essential mineral in processing tungsten for steel alloys used in machine tools and armaments.
• Sweden provided Germany with a major portion, in some war years up to 90-100%, of the iron ore needed for weapons and armoured vehicles and ball bearings.
• Turkey sent chromite, including 100% of Germany's 1943 requirement, for hardening steel to make armour.

Sweden was also criticised in the report for allowing German soldiers to make 250,000 trips across its territory to reach Finland in order to fight against Soviet occupation forces.

The report concluded: "With the exception of Argentina, each of the wartime neutrals made a substantial contribution to the economic foundations of the Nazi war effort."

Trade continued through war

The report said the neutrals' trade with Germany ended only late in the war.

That was partly as a consequence of Allied embargoes and after the US and Britain were forced to try to deny supplies of essential wolfram and chromite by buying them at inflated prices on the open market.