Nahid Taghavi was arrested at her Tehran apartment on October 16 after years fighting for human rights in Iran, in particular for women's rights and freedom of expression, according to the human rights group IGFM.
According to Taghavi's daughter Mariam Claren, the 66-year-old architect is being held in solitary confinement in Tehran's notorious Evin prison.
"I am alarmed for two reasons: her state of health... and the fact that her detention keeps being prolonged," Claren told AFP.
Taghavi's health is "deteriorating rapidly" according to her brother, who lives in Iran and has been allowed phone calls with his sister, Claren said in a statement on Monday.
Taghavi suffers from Type 2 diabetes, Claren said, with her symptoms worsening "after 73 days in solitary confinement in Evin prison and the stress of 73 days of interrogations".
She is now taking the diabetes medication metformin but without further treatment she could suffer "kidney damage, nerve problems, heart attack and stroke", Claren said.
"Enough is enough. She has to be released immediately and unconditionally," she said.
Germany's foreign ministry said in October that it was aware of the arrest of a German-Iranian woman in Iran, but did not name the detained citizen.
"There have been several arrests of German-Iranian dual nationals in the past - including most recently in October 2020, often without comprehensible reasons," it said in an online update of a travel warning in November.
A foreign ministry source told AFP on Tuesday it was continuing to seek consular access to those affected.
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