Iran's foreign ministry summoned on Wednesday Sweden's charge d'affaires to protest the life sentence handed down to a former Iranian prison official over mass executions in 1988.
On Tuesday, a Swedish appeals court upheld the jail term handed down against Hamid Noury, 62, in July last year "for grave breaches of international humanitarian law and murder."
"It is regrettable that the Swedish court, without considering the standards of a fair trial, decided to issue such a destructive verdict," foreign ministry spokesman Nasser Kanani said in a statement.
He condemned the verdict as "fundamentally unacceptable" and said Iran would "use all legal avenues at its disposal" to secure Noury's release.
The foreign ministry later on Wednesday summoned Sweden's envoy to Tehran to voice its "strong protest" against the verdict.
It slammed the Swedish court for citing "false claims" in its verdict.
Noury was arrested at Stockholm airport in November 2019 after Iranian dissidents in Sweden filed police complaints against him.
The case relates to the killing of at least 5,000 prisoners across Iran to avenge attacks carried out by the rebel People's Mujahedin of Iran (MEK) at the end of the Iran-Iraq war of 1980-88.
Noury had worked as an assistant prosecutor in a prison near Tehran at the time but argued that he was on leave during the period in question.
Sweden tried Noury under its principle of universal jurisdiction, which allows it to try a case regardless of where the alleged offense took place.
There have been concerns that the case could have repercussions for the fate of Swedish prisoners in Iran, including EU diplomat Johan Floderus, who has been held for more than 600 days.
Floderus, 33, has been charged with the capital offense of "corruption on earth." He was detained at the Tehran airport in April 2022 on his return from a trip abroad while Noury's original trial was underway.
Another Swedish citizen, dual national Ahmad Reza Jalali, is already on death row in Iran after he was detained in 2016 and sentenced to death on espionage charges.
Swedish media have speculated about the possibility of a prisoner swap between Sweden and Iran. Foreign Minister Tobias Billstrom has declined to comment.
