Russia's Supreme Court on Tuesday rejected an appeal by a scientist sentenced to 15 years in jail for spying for the West, Interfax news agency reported.
The case of Igor Sutyagin, 39, found guilty by a jury in April in the town of Obninsk near Moscow, has provoked an outcry among rights activists who say the nuclear arms expert was punished for carrying out legitimate research.
The Supreme court rejected lawyers' appeal against the make-up of the jury, which had found Sutyagin guilty of passing classified military information to a British firm prosecutors said acted as a front for the US Central Intelligence Agency.
Interfax quoted Sutyagin's lawyer, Boris Kuznetsov, as saying the defence would now take the case to the Strasbourg-based European Court of Human Rights.
Sutyagin, who worked for the elite think tank USA-Canada institute, has insisted throughout the trial he did not possess any classified information he could sell.
He said that information he shared with foreign colleagues came from open sources and that he could not be punished for analysing it.
"I am not guilty," he said after the judge read out his sentence on April 7. "All my guilt is that I had contacts with foreigners. In fact only newspapers, magazines and books, mostly published abroad, were the sources of my works."
Russian human rights campaigners have denounced Sutyagin's sentence of 15 years in a high security jail as a reflection of the government's desire to discourage unauthorised contacts between Russian scientists and the West.