Russia's Audit Chamber has called for an investigation to ascertain what has happened to 350 tonnes of state-owned palladium that was supposed to be deposited in western banks in the late 1990s, according to Russian sources.

The palladium was valued at $3 billion and could be used in the production of auto-catalysts and jewellery.

Vladimir Rybkin, head of the state treasury Gokhran, told Kommersant Daily: "The investigation has not yet begun, but we have just received a request from the audit chamber to provide a series of documents."

Information on pgms in Russia remain a state secret and the Audit Chamber declined to comment on the report, although President Vladimir Putin did sign a decree in March to allow some data to be revealed, according to Reuters.

However figures on state owned pgms held by Gokhran and the central bank are to stay secret for the time being.

It is thought the metal was transferred to the central bank in the mid 1990s, exported in the end of the 1990s and then deposited in several Swiss banks.

What happened to the metal after this point is unknown, although in 1999 there were reports that the central bank had used 300 tonnes of palladium to raise a $3 billion loan.