The authorities in Tehran claimed on Thursday that the man, who was arrested in December accused of espionage, had committed suicide in prison.
The Swiss Foreign Ministry is now demanding that Iran provide "detailed information about the reasons for his arrest and a full investigation into the circumstances surrounding his death”.
It is also emphasized that the return of the man's body is of the highest priority.
The Swiss Foreign Ministry describes the man as a 64-year-old who had traveled to Iran as a tourist. The man had lived in southern Africa and had not been resident in Switzerland for almost two decades. It is unclear when the man was arrested.
Switzerland is said to have been informed of the arrest in December and requested to meet with the man in prison, but the request was denied with reference to the crime suspicion and national security.
In recent years, Iran has arrested several foreign nationals and accused them of espionage in often arbitrary trials. Torture occurs regularly in the country's prisons and hundreds of prisoners are executed every year.
