Belgium submitted a request to Iran on Tuesday that jailed aid worker Olivier Vandecasteele be sent back to his country, which has agreed a prisoner transfer treaty with Iran.
Belgian Vandecasteele was arrested on a visit to Iran in February 2022 and sentenced in January to 40 years in prison and 74 lashes on charges including spying.
Belgium's justice minister has said he was convicted "for a fabricated series of crimes" and in retribution for a 20-year jail term given to an Iranian diplomat in 2021 over a foiled bomb plot.
Iran has said it is open to a prisoner swap, indicating it would seek the return of the diplomat Assadollah Assadi, the first Iranian official to face trial for suspected terrorism in Europe since Iran's 1979 revolution.
The prisoner transfer treaty has been held up by legal challenges brought by the exiled National Council of Resistance to Iran, whose rally near Paris was the target of the foiled bomb plot.
A foreign ministry spokesperson did not reply when asked if the Belgian transfer request was seen as leading to a prisoner exchange.
(Reporting by Marine Strauss; editing by Philip Blenkinsop and Barbara Lewis)