Jafar Panahi was taken into custody nearly two weeks ago by Iranian security forces during a raid on the filmmaker's Tehran home. A state prosecutor has said Panahi's detention is not political and that the filmmaker is suspected of committing unspecified "offenses."
Human Rights Watch noted that Panahi and fellow filmmaker Mohammad Rasoulof, who was picked up along with Panahi, have not been charged since being arrested on March 1. In a statement released Saturday, the rights group also criticized Tehran for providing no legal basis for the filmmakers' continued detention.
"The Iranian authorities should either charge these men or release them immediately," said Sarah Leah Whitson, the rights group's Middle East director.
Human Rights Watch said a third filmmaker was also still in custody. That report could not be independently verified.
Panahi, 49, supported Iran's opposition following the disputed June presidential election in which President Mahmoud Ahmadinejad was declared the winner. He was briefly detained last summer when he visited the gravesides of the victims of Tehran's postelection unrest and was later banned from traveling abroad.
The filmmaker has won awards at the Chicago, Cannes and Berlin film festivals, although several of his films have been banned from showing in Iran.
Whitson said that by targeting a high-profile artist like Panahi, "the Iranian government is sending a clear message that it is willing to go after anyone it considers a threat."
"If well-known figures like Panahi are not immune from arbitrary arrest and detention, ordinary Iranians will think twice before engaging in any activity that may seem critical of the government," Whitson said.
Ahmadinejad's re-election has been challenged by a range of public figures, including filmmakers and singers who have expressed support for the opposition and criticized the harsh government crackdown on street protesters.
The opposition contends Ahmadinejad won through fraud and that opposition leader Mir Hossein Mousavi was the rightful winner.