Iran and Sweden carried out a prisoner swap Saturday that saw Tehran release a European Union diplomat and another man in exchange for an Iranian convicted in Stockholm of committing war crimes over his part in 1988 mass executions in the Islamic Republic.

The arrest of Hamid Nouri by Sweden in 2019 as he traveled there as a tourist likely sparked the detentions of the two Swedes, part of a long-running strategy by Iran since its 1979 Islamic Revolution to use those with ties abroad as…