Mystery drones: Where they have been spotted?

The crux of the federal probe mysterious drone sightings in recent weeks has centered around the skies over New Jersey and New York, but the flying objects controlled by unknown operators has become a global phenomenon.

In the U.S., officials have insisted that the drones do not belong to the U.S. military and are also not the property of foreign governments. But as lawmakers and residents push for more government transparency and answers about what these objects are, the number of places...