Iran had initially accused the Germans, who entered the country on tourist visas, of working illegally as reporters when they interviewed the son of Sakineh Mohammadi Ashtiani, whose death sentence for adultery sparked global outrage.

But the head of the judiciary in Eastern Azerbaijan province said they faced charges of spying, a crime which carries heavy penalties and can be punishable by death.

“The espionage charge for the two German citizens who came to Iran to stage propaganda and spying has been approved,” Malekajdar Sharifi was quoted as saying by the semi-official Fars news agency.

The case has added to strains between Iran and the West as diplomats are talking about resuming negotiations in the coming weeks on Iran’s nuclear program, which some countries believe is aimed at making a bomb — an allegation Tehran denies.

The stoning sentence for adultery received global media attention, with the EU calling it “barbaric,” the Vatican pleading for clemency and Brazil offering Ashtiani asylum.

In an interview with US television in September, President Mahmoud Ahmadinejad denied Ashtiani was ever sentenced to be stoned and accused foreign media of whipping up the story to discredit Iran.

But Sharifi said the stoning sentence had been issued.

“There are various rumours around the Sakineh Mohammadi case and some propaganda has been seen in the media, but the truth is she that has been condemned to stoning for adultery,” he said.

“The delay in carrying out the sentence is because it is a heavy sentence and the case is going through the legal procedure and the execution of the sentence has not been ordered yet.”

A foreign ministry spokesman said in September that the stoning sentence had been suspended but that Ashtiani could be hanged if sentenced for complicity in the murder of her husband.

Iranian television aired an interview with the Germans on Monday in which they said they had been deceived by an Iranian activist in Germany who had persuaded them to do the interview.

The German foreign ministry declined to comment on reports that the detained men are journalists for a German newspaper. A spokesman would only confirm that the two men were German citizens, saying he had “no information” about the nature of their work nor the espionage charges.