(CNN) Nazanin Zaghari-Ratcliffe, the British-Iranian charity worker who was arrested on spying charges in Iran more than three years ago, was transferred Monday from prison to the mental ward of a hospital in Tehran, the Free Nazanin Campaign said in a statement.
Zaghari-Ratcliffe's father visited her in the hospital Tuesday and confirmed that she was being held there under the control of the Islamic Revolutionary Guard Corps.
He was denied access to see her, the campaign's statement said, adding that she has been kept "isolated from family or legal contact under IRGC control for over 36 hours."
Her father was unable to figure out what kind of treatment she was receiving or "the IRGC's agenda in being unexpectedly involved" in her medical care. It is unclear how long she will be held in the mental ward.
Zaghari-Ratcliffe, now 40, was arrested at Tehran airport in April 2016 while trying to return home to London.
She was accused by the Iranian government of trying to overthrow the regime and was sentenced to five years in jail. On June 29 she ended a two-week hunger strike, her third hunger strike since being detained.