Activists behind a website dedicated to revealing secret documents have complained of harassment by police and intelligence services as they prepare to release a video showing an American attack in which 97 civilians were killed in Afghanistan. Julian Assange, one of the founders of Wikileaks, has claimed that a restaurant where the group met in Reykjavik, the capital of Iceland, came under surveillance in March and one of the groups volunteers was detained for 21 hours by police. Assange, an Australian, says he was followed on a flight from Reykjavik to Copenhagen by two American agents. The group has riled governments by publishing documents leaked by whistleblowers. Assange claims surveillance has intensified as he and his colleagues prepare to put out their Afghan film. It is said to concern the so-called Granai massacre, when American aircraft dropped 500lb and 1,000lb bombs ... in Farah province on May 4 last year. Assange complained of covert following and hidden photography by police and foreign intelligence services. There have been thinly veiled threats, he says, from an apparent British intelligence agent in a car park in Luxembourg. Computers were also seized, another member of Wikileaks said ..., raising alarm among supporters: If anything happens to us, you know why ... and you know who is responsible.