The acclaimed Iranian film-maker Jafar Panahi was sentenced to six years in prison today, and banned from directing and producing films for the next 20 years, his lawyer said.

Panahi, an outspoken supporter of Iran's opposition green movement, was convicted of colluding in gathering and making propaganda against the regime, Farideh Gheyrat told the Iranian state news agency, ISNA.

"He is therefore sentenced to six years in prison and also he is banned for 20 years from making any films, writing any scripts, travelling abroad and also giving any interviews to the media including foreign and domestic news organisations," she said. Gheyrat said she would appeal against the conviction.

Panahi won the Camera d'Or at the Cannes film festival in 1995 for his debut feature, The White Balloon, and the Golden Lion at Venice for his 2000 drama, The Circle. His other films include Crimson Gold and Offside. He is highly regarded around the world but his films are banned at home.

Hamid Dabashi, a professor of Iranian studies at Columbia University, told the Guardian the sentence showed Iran's leaders could not tolerate the arts. "This is a catastrophe for Iran's cinema," he said. "Panahi is now exactly in the most creative phase of his life and by silencing him at this sensitive time, they are killing his art and talent.

Dabashi said: "What Iran is doing with the artists, is exactly similar to what Taliban did in Afghanistan. This is exactly like bombing Buddha statues by the Taliban, Iran is doing the same with its artists."

Panahi, 49, was arrested in July 2009 after joining in mourning for protesters killed after the disputed presidential election. He was soon released but denied permission to leave the country. In February 2010, he was arrested with his family and colleagues and taken to Tehran's Evin prison.

Muhammad Rasoulof, one of the film-makers arrested at the same time, was also sentenced to six years in jail today.

Leading Hollywood figures including Martin Scorsese, Steven Spielberg, Francis Ford Coppola and Juliette Binoche condemned his arrest. Binoche held up Panahi's name in protest at Cannes.

In an interview in September, Panahi said: "When a film-maker does not make films it is as if he is jailed. Even when he is freed from the small jail, he finds himself wandering in a larger jail."