Officials say a Russian drone has blasted a hole in an apartment building in northeastern Ukraine during a nighttime attack, killing at least four people and injuring nine others.

Russian first-person view (FPV) drones that use fiber optic cables instead of radio waves to connect with their controllers, making them impervious to jamming and other forms of electronic warfare. The Magyar Birds Brigade claims it has devised a system using mobile radars to provide early warning for incoming FPV drones several kilometers away.