The United States has reiterated demands for the extradition of former Russian nuclear minister Yevgeny Adamov, currently detained in Switzerland.
Adamov said earlier this week that he wanted to be judged for his alleged crimes in Russia.
Folco Galli, a spokesman for the Federal Justice Office, said on Friday that the US was still intent on bringing Adamov to justice.
The former minister is accused by Washington of stealing money intended to improve Russia's nuclear security.
On Tuesday Adamov said he was willing to be extradited to Russia to face trial for his alleged crimes.
But Galli said the former minister would now have to remain in detention in Switzerland until Bern decided which of the two countries had the stronger case.
Adamov has been held in Switzerland since he was arrested on May 2 at the request of the US while visiting his daughter in Bern.
He has since been indicted by a federal grand jury in Pittsburgh, Pennsylvania, on charges of conspiracy to transfer stolen money and securities, conspiracy to defraud the US, money laundering and tax evasion.
Russian authorities, concerned that he could divulge nuclear secrets if extradited to the US, have demanded he be sent to Russia to face charges there.
If the stalemate continues, Switzerland will have to make a decision based on the seriousness and location of the alleged crimes, the dates of the extradition requests and the nationality of the person involved.
The former minister's case has already been heard by the Federal Criminal Court in Bellinzona, which ruled that he must stay behind bars pending a decision on his extradition.
The US accuses him of stealing at least $9 million (SFr11 million) between 1993 and 2003 earmarked for improving Russia's nuclear security. Washington wants him extradited to face fraud charges.
In its own extradition demand, filed later, 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.
He was arrested in the Swiss capital, Bern, on May 2 at the request of the United States.
The US has accused him of embezzling $9 million (SFr11.3 million) that had been destined for nuclear-safety upgrades in Russia.
Russia is also calling for his extradition for the same reasons.
Adamov is not opposed to the Russian extradition request.