Iranian political prisoner Fatemeh Sepehri has said she would only consent to her much-needed heart surgery if her two detained brothers are released.

Ali Sepehri, one of Fatemeh Sepehri's brothers, announced in a tweet on Friday that his sister "requires immediate heart surgery," but she has made the "consent for surgery a precondition" for the release of her detained brothers, Hassan Sepehri and Mohammad-Hossein Sepehri.

"My sister's angiography report shows that two out of her three main heart arteries are more than 95 percent blocked," Mohammad-Hossein Sepehri said earlier in the week. Ali Sepehri says two of his brothers -- Hassan and Mohammad-Hossein -- are in detention.

Sepehri and her brother Mohammad-Hossein are among the signatories of a statement requesting Supreme Leader Ali Khamenei's resignation in 2019. In another letter with 13 fellow women rights activists months later, she called for the abolition of Islamic republic and establishment of a democratic secular government.

She has been arrested a number of times during the past several years. Two years ago, Sepehri was released from Mashhad's Vakilabad prison after nine months of detention, but she released a video, saying "I will not remain silent and will stay on this path."

She was arrested again in the early days of the Women, Life, Freedom protests after security agents raided her home. In October, Sepehri's daughter published a video stating that her mother was held in solitary confinement at the Revolutionary Guard’s Intelligence center in the city of Mashhad.

The Mashhad Revolutionary Court sentenced her to 18 years in prison on charges of "collaboration with hostile states," "assembly and collusion," "insulting the leadership," and "propaganda against the regime." The sentence has been upheld by the Court of Appeals. Based on Article 134 of the Islamic Penal Code, she must serve ten years in prison.