The Swiss federal court has ruled that the former Russian nuclear energy minister, Yevgeny Adamov, is to be extradited to Russia instead of the United States.
The court said it had overturned a decision taken earlier this year by the Swiss justice ministry to extradite him to the US where he faces fraud charges. Adamov is expected to be returned to Russia within the next two weeks.
The court in Lausanne, ruling on Adamov's appeal, concluded that the Russian extradition request had priority according to international law.
In its ruling dated December 22, the court said this would allow the investigation to take place in the country where the alleged crimes took place.
It added that on its own, the US extradition request was not valid under Swiss law because the alleged crimes would have been committed by a foreign functionary in a foreign fiscal system.
The court said extradition for prosecution in the US would only be permitted under Swiss criminal law if it were in tandem with a Russian case, and even then any Russian prosecution would still take priority.
According to the statement, Russian prosecutors have formally guaranteed that they will investigate the US charges against Adamov.
In September, Swiss justice officials gave precedence to the US request because "had priority been given to Russia, Adamov's Russian citizenship would have meant that he could not subsequently have been extradited forward" to the US.
The justice ministry has accepted the court decision, according to spokesman Folco Galli, who said arrangements had already been made with the Russian authorities for the handing over of Adamov.
European treaties on extradition stipulate that it must be carried out within 15 days.
Adamov's lawyer told the Associated Press news agency that the former minister was "delighted and satisfied" by the new ruling.
The Russian government, which condemned the justice ministry's earlier decision to extradite him to the US, also welcomed the court ruling.
The US said it was disappointed by the decision. "We respect the Swiss justice system, but we would have greatly preferred that he be extradited here," said State Department deputy spokesman, Adam Ereli.
Adamov was arrested by the Swiss authorities on a US warrant on May 2, while he was visiting his daughter in Bern.
A US federal grand jury in Pittsburgh, Pennsylvania, indicted the Russian on charges of conspiracy to transfer stolen money and securities, conspiracy to defraud the US, money laundering and tax evasion.
US authorities suspect Adamov of embezzling energy department funds and diverting them into private projects in the US, Ukraine and Russia.
In its own extradition demand, Moscow accused Adamov of fraud between 1998 and 2001 during his term of office.
The ex-minister has not denied he put money into private accounts but has said this was normal practice in Russia to shield money from hyperinflation, an unstable banking system and corruption rife after the collapse of communism.
swissinfo with agencies
Yevgeny Adamov was Russia's atomic-energy minister from 1998 to 2001, when a parliamentary commission accused him of corruption.
He is charged by the US with embezzling funds that had been destined for nuclear-safety upgrades in Russia.
Russia had presented a formal extradition request to the Swiss authorities on May 17, accusing Adamov of fraud.