The Islamic State is getting more sophisticated at weaponizing drones, stoking fears of attacks on civilians.
Officials say the terrorist group has crossed a threshold with its use of unmanned aircraft, using them to drop bombs on Iraqi troops.
But what comes next, and what follows that, is where people are really concerned.
The threat to troops is serious enough to prompt US and Iraqi commanders to issue warnings to soldiers near the front lines. But a far bigger worry, U.S. officials say, is the potential for future attacks against civilians. Islamist militants have long discussed the possibility of using drones as remote-controlled missiles that can deliver explosives or even unconventional weapons such as deadly nerve agents. In recent weeks, the notion of terrorist drones has moved a step closer to reality, terrorism experts say.