Since 1999, more than $600 million connected to the former military leader has been frozen in bank accounts in Switzerland.
The Nigerian government wants all the money released as soon as possible, but Swiss officials say this can't be done until investigations are completed, the BBC said Thursday.
Officials say they hope to return the remaining amount by the end of next year once they have established where the money came from.
General Abacha is believed to have embezzled more than $2 billion from Nigeria while he was in power.
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