Parvin Tajik, the sister of activist Abdolreza Tajik, told Radio Farda on July 7 that her brother was arrested on June 12 after being summoned to Tehran's Intelligence Ministry Office.
Parvin Tajik said the family has not heard from her brother since then, saying they have not even had a "phone call."
"When I eventually managed to meet with Tehran's prosecutor, he strangely enough claimed to be ignorant of my brother's whereabouts," Parvin Tajik said.
She added that the prosecutor asked her when and why Abdolreza Tajik was arrested.
"The prosecutor is the only legal authority who can issue arrest warrants," Parvin Tajik noted. "His ignorance [about the case] shows that my brother's arrest was against the law and can therefore be considered an abduction."
She said it also shows that her brother's life is in danger.
Parvin Tajik said she went to look for her brother at Tehran's Evin prison, the notorious jail where political prisoners are often kept. She said she was told her brother's name was not registered at the institution.
Parvin Tajik said she still does not know the charges on which her brother was arrested after he was summoned to the Intelligence Ministry.
A member of the Tehran-based Defenders of Human Rights Center (DHRC), Abdolreza Tajik's latest detainment was the third time he has been arrested since the June 2009 presidential election.
Abdolreza Tajik was first taken into custody shortly after the election and released after 46 days in Evin prison. He was rearrested on December 29.
Nobel Peace Prize laureate Shirin Ebadi, who is also the head of the DHRC, told Radio Farda on July 5 that she has grave concerns about Abdolreza Tajik's condition.
"If anything happens to him, [Iran's] judiciary chief is directly responsible," Ebadi said