How the Neda film went viral Mentorn Media for HBO

Iran is jamming satellite broadcasts in attempts to stop people seeing a new film telling the story of Neda Agha-Soltan, the young woman who was shot dead during the mass protests that followed last summer's disputed presidential election.

Viewers in Tehran complained of jamming and power cuts on Wednesday and yesterday when the Voice of America Persian TV network broadcast the documentary For Neda, featuring the first film interviews with the family of the 27-year-old.

The 70-minute film, made by Mentorn Media for HBO and being screened in the US this month, has rapidly gone viral in Iran in the run-up to next Saturday's anniversary of the disputed elections that triggered the protests. It is available on YouTube so can be seen by anyone with access to the internet.

Street protests began shortly after the polls closed on 12 June last year, when the incumbent hardliner, Mahmoud Ahmadinejad, claimed victory over the Green movement leader, Mir Hossein Mousavi, triggering claims that the vote had been rigged.

Neda became an instant symbol of Iran's struggle for democracy. On 20 June, within hours of her killing – described as "probably the most widely witnessed death in human history" – mobile phone images of her bloodstained face were being held up by demonstrators in Tehran and all over the world.

The film was directed by Antony Thomas and co-produced by Saeed Kamali Dehghan, a former Guardian correspondent in Iran. Kamali Dehghan risked arrest to interview Neda's parents and siblings and obtain unseen footage of her life.

Witnesses have said that she was shot in the heart by a sniper with the Basij militia force, who has been named as Abbas Kargar-Javid.

Iran's intelligence ministry is reportedly due to release its own documentary to remove "ambiguities" surrounding her death and provide "new evidence" about what it calls the west's version of events.

Neda's family were under pressure to cooperate with the official documentary but refused. Two of her friends were forced to participate.

It is not clear whether the official film is the same as one produced earlier this year by Iranian state TV. That suggested that Neda was an agent of the US and Britain who staged her own death and poured blood on her face. BBC Tehran correspondent Jon Leyne was also blamed for her killing before being expelled.

HBO says it took the unprecedented decision to pre-release the film for Iranian audiences because of its relevance in the run-up to the anniversary of the polls.

Ahmadinejad today warned the opposition of tough measures, ahead of protests next week. "Those who want to tarnish the image of the country and its system will be removed from the [political] scene," he said in a speech marking the 21st anniversary of the death of Ayatollah Khomeini, architect of the 1979 Islamic revolution, which toppled the shah.

"The election last year was the most democratic in the world as nowhere else would 40 million people turn up for elections," he claimed. Ahmadinejad pledged: "Whoever stands against the Islamic system will not survive." Ayatollah Ali Khamenei, Khomeini's successor as supreme leader, boasted that Iran, facing new UN sanctions over its nuclear programme, was in a position to "see off any conspiracies".

Mehdi Karroubi, a defeated reformist candidate, was attacked and heckled by hardliners when he visited the shrine yesterday. "Whoever objects to fraud in the election is accused of being a Mossad or CIA agent," he said. "The fate of the election is in the hands of the Basijis and revolutionary guards." Karroubi warned on his website that the Islamic regime was being ruined. "They speak as if Imam [Khomeini] belongs to them only and others have broken path with the imam."