In a petition signed by filmmakers and actors such as Robert De Niro and Robert Redford, the group denounced the March arrest of Panahi, whose movies include "The White Balloon" and "The Circle."
"We … stand in solidarity with a fellow filmmaker, condemn this detention, and strongly urge the Iranian government to release Mr. Panahi immediately," the petition says.
Panahi, a maker of gritty films that examine social issues in the Islamic Republic, was a supporter of Iranian opposition leader Mirhossein Mousavi in last year's disputed election that saw President Mahmoud Ahmadinejad retain power.
On March 1, Panahi, his wife, daughter and 15 guests were held by Iranian security guards at his home, according to opposition leaders.
The petitioners say Panahi has since been held in Tehran's Evin prison, and they cite a letter from Panahi's wife expressing "deep concerns about her husband's heart condition, and about his having been moved to a smaller cell."
"Like artists everywhere, Iran's filmmakers should be celebrated, not censored, repressed and imprisoned," the petition reads.
Panahi, 49, saw his first film, 1995's "The White Ballon," win the Camera d'Or prize at the Cannes film festival, and 2000's "The Circle," which looked at the treatment of women in Iran, earned the top prize at the Venice film festival.
Other filmmakers signing the document include brothers Joel and Ethan Coen, Jonathan Demme, Ang Lee, Oliver Stone and documentary maker Michael Moore.
(Editing by Mohammad Zargham)
