LONDON — Concern is growing for the well-being of Iranian helmer Jafar Panahi, a vocal supporter of opposition leader Mir Hossein Mousavi. Panahi was arrested at his Tehran home March 1 along with fellow filmmakers and family members.

More than two weeks after the arrest, Panahi has yet to be charged, and his family and lawyer say they have had no access to the filmmaker, who has had frequent run-ins with the Iranian authorities.

Other activists and artists arrested by the authorities in the wake of massive anti-government protests in June have complained of mistreatment and harsh interrogations while in prison to extract “confessions.”

Panahi’s wife, Tahereh Saeedi, and their daughter were among those rounded up in the March 1 action but were released two days later, as were 12 other members of the group.

However, Panahi and fellow filmmakers Mohammad Rasoulof (writer-director of 2009’s “The White Meadows”) and Mehdi Pourmoussa (assistant director on Rafi Pitts’ “The Hunter,” which was made against the backdrop of last year’s disputed presidential elections) remain behind bars in Tehran’s Evin prison.

Weekend reports on opposition websites Kaleme and Rahesabz said the authorities had released Rasoulof for 20 days on bail of $100,000, but this could not immediately be confirmed.

With the entire country shut down for the Persian New Year on March 21, little movement is expected in Panahi’s case for the foreseeable future.

The Iranian media has said Panahi was picked up for making a film about anti-government protests that rocked Iran after Mousavi and other opposition leaders contended that the June 12 re-election of President Mahmoud Ahmadinejad was rigged.

Conservative news website Tabnak said Panahi was producing “an anti-regime film with his colleagues but the security apparatus vigilantly discovered their moves and they were arrested.”

Panahi’s son Panah insists his father was doing nothing illegal.

“My father has not made any anti-regime films nor has he made a film about recent events,” he told the Kaleme.com website. The arrests, he added, took place “while they were shooting a film with permission.” He did not elaborate.

Tehran chief prosecutor Abbas Jafari Dolatabadi has shed little light on why the filmmaker is being held.

Panahi, he said, was not arrested for political reasons or because he is an artist but because he is “accused of some crimes and arrested with another person following an order by a judge.”

Few doubt, however, that Panahi was picked up for his staunch support for Mousavi, himself an architect, artist and painter and therefore part of the artistic community distrusted by the Iranian regime.

Celebrated Iranian filmmaker Abbas Kiarostami published an open letter in a Tehran newspaper calling for the release of Panahi and Rasoulof. In the letter, republished in English on a New York Times blog, Kiarostami blames the Ministry of Guidance and Islamic culture for the parlous state of Iranian cinema, and says it is “directly responsible for what is happening to Jafar Panahi and his like.”

U.S.-based Human Rights Watch called on Iran to either charge or release the filmmaker, saying 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.”

Golshifteh Farahani, who in 2008 appeared in “Body of Lies,” also condemned the arrest.

“We are angry,” she said from Paris where she now lives in exile after being hounded by the Iranian authorities for starring in the Hollywood movie. “Jafar is one, maybe the only one, still in Iran who is talking. Most artists (in Iran) don’t talk because they would rather work somehow. I appreciate that, but Jafar is the one who had the courage to talk, and he talked for everyone.”