Filmmaker Omer Fast was looking to talk to US drone pilots in order to shed light on the highly-controversial practice of remote-controlled killings taking place in the Middle East and Asia. But the Israel-born, Berlin-based artist was stopped dead in his tracks when his producer got a call from the FBI after posting an anonymous ad on Craigslist.

Last week, in an interview with Photoworks magazine, Fast claimed that he and his team were "told to stop what we were doing and threatened in suggestive, spy-movie language" while doing research for his short film, 5,000 Feet Is The Best. Fast's Craigslist ad sought contacts from Creech Air Force Base, a major drone operations center just outside Las Vegas, Nevada.

"It sure took us by surprise because they had to trace our phone number via the IP address."

"I imagine it's probably quite a routine thing for them to do but it sure took us by surprise because they had to trace our phone number via the IP address used to publish an otherwise anonymous ad on Craigslist," Fast said in an email with The Verge. After receiving the call, he says that a vast majority of their contacts suddenly dropped off. In the end it was only a minor setback, however — Fast says he was able to re-publish the ad, and no one was waiting for him when he landed in Las Vegas during production. But the alleged intimidation tactics — which the FBI has not commented on at this time —remain a potentially chilling example of the US government's efforts to protect information regarding its use of unmanned aerial drones.

Granted, the threats are not totally unexpected given the highly secretive nature of the US drone program. To date, President Obama has only briefly acknowledged the ongoing campaign, describing the targeted killings as "surgical" in nature despite overwhelming evidence that they are anything but. The administration's views on the matter also tend toward the extreme: Obama's pick to replace former CIA head David Patreaus is John Brennan, the White House's top counterterrorism advisor who manages the secret "kill list" used in determining targets for US drone strikes, and who once made the dubious claim that "there hasn't been a single collateral death" in the decade and change since drones began doing targeted killings in Pakistan, Yemen, and elsewhere.

In the past, the US government has been accused of using other, more intense forms of coercion against drone critics. Imran Khan, a popular Pakistani politician and potential candidate for Prime Minister who has voiced opposition to the drone program was detained by US officials after boarding a flight to New York. Another prominent critic, Pakistani lawyer Shahzad Akbar, has canceled speaking engagements in the US after been repeatedly denied a visa.

Fast says the goal of his project, released in 2011, was to "better understand the deployment of drones." The film itself, however, takes a less straightforward approach, using interviews with two drone pilots as the backdrop for a short narrative cocktail of reality, fiction, and fantasy.