The Iranian Revolutionary Guard accused a British-Iranian aid worker who has been detained since early April of trying to "overthrow" the government in a statement published on Wednesday.
Nazanin Zaghari-Ratcliffe is a 37-year-old program coordinator with the Thomson Reuters Foundation, a London-based charity.
Iranian Revolutionary Guard officials detained Zaghari-Ratcliffe on April 3 when she arrived at an airport to fly back to Britain, according to her husband Richard Ratcliffe.
"This person had membership in foreign companies and organizations and planned and carried out media and cyber projects with the intent of a soft overthrow of the holy Islamic Republic government," the statement said. It was published by a Guard office in Kerman province, where Zaghari-Ratcliffe is being held.
Zaghari-Ratcliffe "carried out criminal activities with the guidance and protection of media and spy services of foreign governments," according to the statement. She was arrested after "massive intelligence operations" by the Guard.
Richard Ratcliffe dismissed the accusation that Nazanin was trying to bring down the government as "preposterous."
"To my understanding there are still no formal charges. It seems like this is a political case," he said.
Ratcliffe said the family had contact with Nazanin earlier this week and she'd been moved to Evin prison in Tehran.
Monique Villa, the Chief Executive of the Foundation, said that Nazanin has been employed for four years as a project coordinator in charge of grant applications and training, and had no dealing with Iran in her professional capacity.
"The Thomson Reuters Foundation has no dealings with Iran whatsoever," she said, and has no plans to.
Villa said that Nazanin "had traveled to Iran in a personal capacity. She was on a family holiday with her two-year-old-daughter Gabriella."
The Foundation, Villa said, was in close contact with Nazanin's family as well as with the British Foreign Office.
The Foundation operates independently from Reuters News.
Britain's Foreign Office said it is following up the allegations made in the statement.
"We are urgently seeking information from the Iranian authorities on the reported accusations being made against Ms Zaghari-Ratcliffe," a spokesperson for the Foreign Office told Reuters. "We have raised this case repeatedly and at the highest levels and will continue to do so at every available opportunity."
No charges have been filed in the case, but Zaghari-Ratcliffe has told family members in Iran that she was forced to sign a confession under duress, her husband said last month.
Zaghari-Ratcliffe's file has been sent to Tehran to begin judicial proceedings but officials from the intelligence wing of the Revolutionary Guard are still interrogating her, according to the statement.
Iran does not recognize dual-citizenship and if Zaghari-Ratcliffe is charged she will be tried as an Iranian citizen.
The Guard statement said that Zaghari-Ratcliffe was arrested by the intelligence wing of the Revolutionary Guard at the Imam Khomeini international airport in Tehran and subsequently transferred to Kerman in southeast Iran.
(Edited by Simon Robinson)