(Bloomberg) -- Iran released Belgian aid worker Olivier Vandecasteele in a prisoner swap for a diplomat convicted of a bomb plot in Europe.

Vandecasteele has undergone medical examinations in Oman and will return home on Friday night, Belgian Prime Minister Alexander De Croo said. A former employee of the Norwegian Refugee Council in Iran, Vandecasteele had been detained since February 2022 and was sentenced to 40 years in prison on espionage and money laundering charges.

Belgium in turn released Asadollah Asadi, Iranian Foreign Minister Hossein Amirabdollahian said in a tweet. Asadi is a diplomat who was arrested in 2018 for his alleged role in a plot to bomb an Iranian opposition rally in France.

Gulf sultanate Oman said on Friday that it brokered a prisoner exchange between Iran and Belgium, without naming the prisoners involved. Oman has been a frequent mediator with Iran, playing a role on issues ranging from prisoner swaps to the nuclear deal with world powers.

Read more: Iran Frees French, Irish Prisoners Held on Security Charges 

Rights groups say the Islamic Republic detains foreign and dual nationals on national security charges in order to extract concessions from western governments.

--With assistance from Kevin Whitelaw.

(Updates with name of Iranian prisoner in fourth paragraph.)

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