A federal grand jury in North Carolina is investigating allegations the controversial private security firm Blackwater illegally shipped assault weapons and silencers to Iraq, hidden in large sacks of dog food, ABCNews.com has learned.

Under State Department rules, Blackwater is prohibited from using certain assault weapons and silencers in Iraq because they are considered "offensive" weapons inappropriate for Blackwater's role as a private security firm protecting US diplomatic missions.

"The only reason you need a silencer is if you want to assassinate someone," said former CIA intelligence officer John Kiriakou, an ABC News consultant.

Six Blackwater employees are under investigation by another federal grand jury, in Washington, D.C., in connection with the shooting deaths of at least 17 civilians in September 2007 at a Baghdad traffic circle. Prosecutors are expected to return indictments in the next few weeks, according to people familiar with the case.

 New Blackwater Iraq Scandal: Guns, Silencers and Dog Food (by Brian Ross and Jason Ryan, ABC News)