Switzerland demanded on Friday that Iranian authorities provide more information on the death of a Swiss national in an Iranian prison the day before.

The Swiss Department of Foreign Affairs (FDFA) said it had been informed of the 64-year-old man's arrest on December 10 on suspicion of espionage.

"Switzerland is demanding that the Iranian authorities provide detailed information on the reasons for his arrest and a full investigation into the circumstances of his death," the FDFA said in a statement.

France protests three 'hostages' in Iran

Also on Friday, France summoned Iran's ambassador to protest the years-long detention of three of its citizens, with the Foreign Ministry saying their conditions were tantamount to torture, and calling them "hostages of the state of the Islamic republic of Iran." 

"Their situation is unbearable, with undignified detention conditions that, for some, constitute torture under international law," the Ministry said. 

Officials in France have adopted a harder tone towards Tehran in recent weeks, both on the detention of European citizens and other issues like Iran's nuclear program. 

Senior French, British and German diplomats are set to meet their Iranian counterparts in Geneva on Monday to discuss bilateral issues and the potential future of nuclear talks, in probably the last meeting of its kind before Donald Trump's return to the White House on January 20. 

French Foreign Minister Jean-Noel Barrot spoke about the prisoners earlier in the week, saying their situation was worsening.

What do we know about supposed suicide?

The Swiss national was being detained in prison around 180 kilometers (110 miles) east of Tehran.

The man had been traveling in Iran as a tourist at the time of his arrest, the FDFA said. The ministry added that he had not resided in Switzerland for some 20 years. He had been living in southern Africa.

The chief justice of Iran's Semnan province was quoted by the judiciary news agency Mizan as saying that the man took his own life in prison on Thursday.

The FDFA said it was seeking the repatriation of his body, expecting this to take place in the next few days.

"The repatriation of the body to Switzerland is also a top priority," the FDFA said.

The ministry said that the Swiss embassy had tried to speak with the man after being informed of his arrest, but that the request was denied amid the ongoing Iranian probe.

Other foreign nationals arrested in Iran

Switzerland plays an important intermediary role between the United States and Iran.

Several dual and foreign nationals have been arrested in Iran in recent years, often on espionage charges, in what rights groups say is an effort by Tehran to extract concessions from their respective countries. Iran has denied such accusations.

Late last year, Iran announced the execution of German-Iranian software developer Jamshid Sharmahd, who was convicted over his alleged role in the 2008 mosque bombing in the southern Iranian city of Shiraz, which killed 14 people.

Tehran later said that Sharmahd had died before the death sentence could be carried out.

rmt/msh (AFP, Reuters)