"Ahmadreza Djalali is being held under very harsh conditions, and his poor health is deteriorating further. This is deeply concerning," Sweden’s foreign minister Maria Malmer Stenergard said in a statement on Friday.
"The government demands that Iran immediately release Ahmadreza Djalali on humanitarian grounds so that he can be reunited with his family," she added.
The statement came as Djalali marked nine years since his arrest in Iran and issued a direct plea to Sweden’s prime minister and the European Parliament in a message from Tehran's Evin prison.
"I am at my breaking point. 3,288 days of suffering and being under risk of execution, showed the inefficacy of words and condemnation," Djalali said.
"If I die here, either due to execution or illness, the officials who were careless and neutral about my situation over all these years and left me behind when they were able to return me home are also responsible in my death," he added.
Djelali was convicted of "corruption on earth" for allegedly spying for Israel by an Iranian revolutionary court in 2017 but said authorities used torture to coax his confession, which was subsequently repeatedly broadcast on state media.
He also criticized the prisoner swaps between Iran and Belgium, and between Iran and Sweden, saying, "In both events, I was used as a bargaining chip but I was left behind without trade and discriminately during the swap of Assadi and Nouri with Belgian and Swedish prisoners in Iran."
As part of a prisoner exchange agreement last year in June, Sweden repatriated a former Iranian official convicted of war crimes, Hamid Nouri, in exchange for the release of two Swedish citizens, Johan Floderus, an EU representative, and Saeed Azizi, who had been detained in Iran on charges of spying for Israel.