It's always wrong (in every possible way) to be the first one to engage hostilities. To be morally in the clear, you should always wait for the other side to engage first. If we didn't follow this doctrine, we would've already had a nuclear holocaust. Warmongers and civilization don't mix.
We don't know anything about their capabilities as individual drones or as a cluster of drones. For all you know, when you shoot one, the other ten take that as declaration of war.
We should follow the drones to see where they land, and continue the investigation from there.
There is no evidence that the drones carry WMDs, or that they're dangerous like Iran. If we had reason to believe that the drones are associated with WMDs, then it would be okay to neutralize them, but we don't. Because of false assertions about WMDs, we've already had one unnecessary war in Iraq. How many more do you want?
We don't know anything about their capabilities as individual drones or as a cluster of drones. For all you know, when you shoot one, the other ten take that as declaration of war.