The Iranian-based Human Rights Organization of Kurdistan says its members are being prosecuted because of their human rights activities, RFE/RL's Radio Farda reports.
The organization's spokesman, Jalal Aghvami, told Radio Farda on April 6 that the latest example is the case against Kaveh Ghasemi Kermanshahi.
Aghvami said Kermanshahi was detained in Tehran on February 3. He was supposed to be released after one month, but his release was repeatedly postponed. The charges against him are unclear.
Aghvami said Kermanshahi's detention has been extended again for a another month.
"Kaveh's family has been told he will be detained...until May 5, without any reason being given," Aghvami said.
He also mentioned the case of Mohammad Sadigh Kabudvand, the head of the Human Rights Organization of Kurdistan. Aghvami said Kabudvand was arrested in 2008 and is serving an 11-year prison sentence.
"Although suffering from several illnesses, Kabudvand has not been allowed to leave [prison] on a temporary release for medical treatment," Aghvami said.
The Human Rights Organization of Kurdistan is one of the most influential rights groups in Iran's Kurdish regions.
According to official figures, Kurds account for roughly 10 percent of Iran's population and live mainly in the western part of the country.
Kurdish political groups have repeatedly come under pressure from the Iranian authorities and their activists arrested.