Norway has freed a Russian suspected of spying, as Moscow demanded an apology from Oslo.

Mikhail Bochkaryov was detained last month at the Oslo airport after participating in a seminar in Norway's parliament.

After leaving an Oslo prison October 19, Bochkaryov said he was "feeling better now than before his release."

Authorities accused Bochkaryov, who works in the Russian parliament's upper chamber, of collecting data on the building and its network. He denied any wrongdoing.

A Norwegian court ordered his release on October 18, after ruling that investigators had failed to substantiate their case. But Bochkaryov was kept in custody after the national police agency appealed the decision.

Prosecutor Kathrine Tonstad told Norwegian television that an investigation is continuing.

"No decision has been made on whether to file any charges. He is free to go home," she said October 19.

Reports had said Bochkaryov might be used as leverage in efforts to obtain the release of a Norwegian held in Russia on suspicion of spying.

Frode Berg was arrested in April and is still awaiting trial after reportedly admitting to having helped Norwegian intelligence by acting as a courier.

Russia demanded Oslo throw out "the absurd charges." And the Russian Embassy in Oslo said in a post to its Facebook page that "an official apology" from Norway was expected.

With reporting by Reuters and TASS