Brad Pitt isn't a terrorist — but he's certainly being treated like one.

On Monday, a SWAT team raided a Budapest warehouse holding weapons being used in Pitt's upcoming zombie movie World War Z. "The film is already over budget and over schedule," a source tells Us Weekly. "Brad is furious."

Police seized 85 fully-functional weapons, most of which were automatic, military-style assault rifles. "We can confirm that weapons were confiscated at an airport," Hajdu Janos and Zsolt Bodnar, the director and deputy director of Hungary's Anti-Terrorism Unit, tell Us.

The problem, a source says, is that the guns came with paperwork claiming they were non-functional — but they're actually in working order.

"This morning a private plane brought guns wrapped in a parcel from a company to an individual [in Budapest]," Janos and Bodnar add. "Guns like these are highly illegal to transport even if they were to used as stage guns, which hopefully they weren't."

According to a source, Pitt, 47, isn't to blame for the prop problem. "The movie company's employees must have made a mistake bringing the guns in without the Anti-Terrorism Unit's permission."

Janos adds: "We are interrogating witnesses now, getting closer to solving the firearms story."

Pitt's company, Plan B Entertainment, is producing World War Z. It is scheduled for a December 2012 release.