The FBI is warning law enforcement agencies across the country that the Ferguson grand jury decision "will likely" lead some extremist protesters to threaten and even attack police officers or federal agents.

Peaceful protesters could be caught in the middle, and electrical facilities or water treatment plants could also become targets. In addition, so-called "hacktivists" like the group "Anonymous" could try to launch cyber-attacks against authorities. ABC Chicago reports.

The bulletin's conclusions are blunt: "The FBI assesses those infiltrating and exploiting otherwise legitimate public demonstrations with the intent to incite and engage in violence could be armed with bladed weapons or firearms, equipped with tactical gear/gas masks, or bulletproof vests to mitigate law enforcement measures."

The bulletin cites a series of recent messages threatening law enforcement, including a message posted online last week by a black separatist group that offered "a $5,000 bounty for the location" of Ferguson police officer Darren Wilson, who fired the shots that killed Brown on Aug. 9.

In its new intelligence bulletin, obtained by ABC News, the FBI says "exploitation" of mass demonstrations "could occur both in the Ferguson area and nationwide."