WikiLeaks founder Julian Assange has described a forthcoming Hollywood film about him as a "massive propaganda attack" during a video-linked talk to students at Oxford University.

Assange said he had seen a copy of the script for The Fifth Estate, which stars Sherlock's Benedict Cumberbatch and is directed by Dreamgirls' Bill Condon. Addressing the Oxford Union from his refuge at the Ecuadorian embassy in London last night, the activist also described the film as an inflammatory attack on Iran.

The first picture of Cumberbatch as Assange was released yesterday, featuring Cumberbatch standing alongside Goodbye, Lenin!'s Daniel Brühl, who is playing the activist's confidant Daniel Domscheit-Berg. The Fifth Estate, which focuses on the early days of WikiLeaks, is based on Domscheit-Berg's book Inside WikiLeaks: My Time with Julian Assange at the World's Most Dangerous Website, as well as Guardian writers David Leigh and Luke Harding's WikiLeaks: Inside Julian Assange's War on Secrecy.

Assange told the Oxford Union that Condon's film began with scenes inside a military complex in Iran, where nuclear symbols could clearly be seen. The suggestion, he said, was that the country was building a nuclear weapon and the film was clearly an attempt to go about "fanning the flames" of war. "How does this have anything to do with us? It is a lie upon lie," he said. "The movie is a massive propaganda attack on WikiLeaks and the character of my staff."

Assange, who held a purported copy of the script for The Fifth Estate by The West Wing's Josh Singer in his hand throughout, though didn't show it to the camera, also quoted from a scene in which he said scientists were seen meeting a US agent. "How is it that a lie gets into a script about WikiLeaks?," he asked.

Condon had earlier issued a statement via studio Dreamworks in which he said: "It may be decades before we understand the full impact of WikiLeaks and how it's revolutionised the spread of information. So this film won't claim any long view authority on its subject, or attempt any final judgment. We want to explore the complexities and challenges of transparency in the information age and, we hope, enliven and enrich the conversations WikiLeaks has already provoked."

Assange is currently living in the Ecuadorian embassy, which offered him asylum in August, in an effort to avoid being extradited to Sweden, where he faces allegations of rape and sexual assault. He says he fears being extradited onwards to the US over his WikiLeaks activism. The Fifth Estate, also starring Laura Linney, Anthony Mackie, David Thewlis and Peter Capaldi, is due to be released in the US in November, the timing of which suggests an awards-season run in 2014.