Former Russian atomic energy minister Yevgeny Adamov, who is accused of fraud, must remain in Swiss custody pending a decision on his extradition.
The Swiss Federal Criminal Court on Thursday turned down two appeals by Adamov to be set free.
Adamov, who has been in detention since May, is the subject of two extradition requests – one from the US and the other from Russia.
The court in Bellinzona ruled that there was no evidence to suggest that the US proceedings had been initiated for political reasons.
Regarding the Russian extradition request, the court's judges found that Adamov had no immunity on Swiss territory.
Adamov now has 30 days to appeal against the rulings to the Lausanne-based Federal Court, the highest court in the land.
Meanwhile the Federal Justice Office has to decide where Adamov should be extradited. But an appeal against this decision could also be lodged with the Federal Court.
In an earlier ruling in June the Federal Criminal Court had ordered Adamov's release on the grounds that he should never have been arrested. But he remained in custody after intervention by the justice ministry.
Adamov was arrested in Bern on May 2 on a US warrant while on a visit to answer questions in an unrelated court case about the financial activities of his daughter, a Swiss resident.
The US accuses him of stealing at least $9 million (SFr11.24 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.
Russia has expressed concern over Adamov's arrest, which it believes fails to comply with international law.
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 $9 million, which had been destined for nuclear-safety upgrades in Russia, and transferring the money to various US companies under his control.
The Americans have filed a demand for his extradition.
Adamov also faces extradition to Russia, which handed a formal request to the Swiss authorities on May 17, on fraud charges.