The family of the late Nigerian dictator, Sani Abacha, has appealed against Switzerland's decision to hand over to Nigeria funds frozen in Swiss banks.
The appeal follows a decision in August to return the remainder of Abacha's assets, worth SFr622 million ($500 million), which the Swiss say are of "criminal origin".
The Abacha family's lawyer, Bruno de Preux, said he had filed an appeal against the planned handover of funds at the Federal Court in Lausanne on Monday.
The money will have to remain frozen until the court rules on the appeal.
It is the second time that members of the Abacha family have attempted to block Swiss cooperation with Nigeria. Previously they went to court to try and prevent the two countries from sharing information about the late dictator's assets.
That appeal was thrown out, paving the way for the transfer of the frozen funds, which was approved by the justice ministry last month.
The return would bring an end to six years of searching for an estimated $3 billion in assets allegedly embezzled and transferred abroad by Abacha.
The Swiss said in August that the money was clearly of criminal origin and should therefore be returned.
The family had 30 days to appeal against the handover of the funds, and their lawyer had made clear they would do so.
He said at the time that there was no proof that the funds were “of criminal origin”.
For his part, the lawyer representing the Nigerian government in Geneva, Enrico Monfrini, praised the Swiss for their cooperation and said that other countries, such as Britain, were dragging their feet.
The money is part of the $700 million frozen by the Swiss authorities in 1999 after Nigeria asked for assistance in investigating the financial network allegedly set up by Abacha.
Nigeria believes that Abacha, who died of a heart attack in 1998, siphoned off the $3 billion funds, which he invested in several countries abroad including Britain and Switzerland.
Switzerland returned a total of $200 million to Nigeria at the end of 2003 following settlements between the parties to the money and the Nigerian authorities, as well as seizure orders issued by the Geneva prosecutor’s office.
The justice ministry said that further information and documents had allowed it to piece together the paper trail left by the additional $500 million.
Nigerian officials - including President Olusegun Obasanjo - have said that the returned funds would be used for health, education, roads and other projects "to help rural and poor people".
Swiss officials said the country's mission in Nigeria would "monitor the use of the Abacha funds in accordance with this assurance".
swissinfo with agencies
According to Nigeria, Abacha siphoned off $3 billion in funds.
In Switzerland, SFr870 million ($700 million) of this missing money has been found.
The Swiss will give back the money in two stages: around $200 million has already been handed over, $500 million is still to come.
The Abacha money was found in 19 Swiss banks.
The Federal Office of Justice said the greater part of the funds frozen in Switzerland since 1999 were of criminal origin.
The Abacha family has appealed the decision, at the Federal Court.