WASHINGTON — Kurdish forces fighting the Islamic State in northern Iraq last week shot down a small drone the size of a model airplane. They believed it was like the dozens of drones the terrorist organization had been flying for reconnaissance in the area, and they transported it back to their outpost to examine it.

But as they were taking it apart, it blew up, killing two Kurdish fighters in what is believed to be one of the first times the Islamic State has successfully used a drone with explosives to kill troops on the battlefield.

In the last month, the Islamic State has tried to use small drones to launch attacks at least two other times, prompting American commanders in Iraq to issue a warning to forces fighting the group to treat any type of small flying aircraft as a potential explosive device.

The Islamic State has used surveillance drones on the battlefield for some time, but the attacks — all targeting Iraqi troops — have highlighted its success in adapting readily accessible technology into a potentially effective new weapon. American advisers say drones could be deployed against coalition forces by the terrorist group in the battle in Mosul.