The United Nation's security council unanimously approved Paul Volcker's inquiry into the scheme that US legislators say allowed billions of dollars in illegal oil revenue to flow to Saddam Hussein.

Kofi Annan, the UN secretary general, said yesterday that he took the allegations seriously. "I want to get to the truth and ... I am happy they are taking on this assignment."

In Washington a panel of Bush administration officials involved in the programme told the House government reform subcommittee there had been a widespread system of kickbacks benefiting officials within Iraq, including Saddam.

However, they said there was no corroborated evidence so far suggesting UN officials had been part of the scam.

Mr Volcker will lead the three-person investigative panel, which also includes the Yugoslav war crimes prosecutor Richard Goldstone of South Africa and the Swiss criminal law professor Mark Pieth.

It will rely on voluntary cooperation from foreign governments, UN staff, members of Saddam's former government and Iraqi leaders.

The investigative arm of Congress had estimated that the Iraqi government pocketed $5.7bn by smuggling oil to its neighbours and $4.4bn by extracting illicit surcharges and kickbacks on otherwise legitimate contracts.

The allegations first surfaced in January in the Iraqi newspaper al-Mada, which listed 270 former government officials, activists and journalists from more than 46 countries suspected of profiting from the UN programme.