Iranians living in Sweden gathered outside the Ministry of Foreign Affairs on Sunday to protest the release of an Iranian official serving a life sentence for war crimes.

Hamid Nouri was in prison for his involvement in the 1988 massacre of thousands of Iranian political prisoners, and was released over the weekend in exchange for two Swedish citizens, one of whom was an EU diplomat accused of spying for Isreal.

The protest also highlighted the case of Ahmadreza Jalali, an Iranian-Swede who was left out of the prisoner swap and remains on death row in Iran.

Among the speakers of the rally was Jalili’s wife Vida Mehrannia who criticized Swedish Prime Minister Ulf Kristersson for agreeing to the exchange which only emboldens Iran's policy of hostage taking.

"The Swedish government has claimed that the Islamic Republic is not willing to agree to exchange Ahmadreza Jalali. How, then, was the Swedish government prepared to release a terrorist?" she questioned.

The protest in Stockholm is part of a larger wave of dissent, with many fearing that such exchanges may embolden the Iranian government in its use of hostage-taking as a diplomatic tool.

It is unknown how many dual-nationals are being held in Iran, but earlier this month it was revealed that a British-Iranian woman was the latest to have been found being held in Evin Prison on trumped up charges.

Nasrin Roshan was arrested on her way home to Britain accused of protesting against the government abroad, sentenced to three years in prison.

Just last year, the US exchanged five US-Iranians for the release of $6bn of frozen Iranian funds held in South Korea, further legitimizing Iran's policy of hostage-taking.