A spokesman for the new head of state General Abdulsalami Abubakar said the money had been taken from the national treasury under the false pretence of paying back debts owed to Russia in the construction of a giant steel factory.

Spokesman Mohammed Haruna said debts accrued to Russia in the construction of the Ajaokuta steel plant were grossly overvalued.

No steel

He alleged that members of the Abacha family pocketed the difference. He also said that two former government ministers had made "useful" statements to the police in connection with the investigation.

Correspondent Barnaby Phillips says General Abubakar seems determined to give the impression that gross corruption will no longer be tolerated in Nigeria.

Our correspondent says the Ajaokuta steel plant is one of Africa's most disastrous development projects.

Although construction began in the late 1970s, and has dragged on at enormous cost for two decades, it has never produced a single piece of steel.

Missing millions

Last month, the government said it had retrieved about $750m in different currencies from Gen Abacha's family.

The amount included $625m in dollar notes and another £75m ($125m) in pounds sterling.