Ukraine claimed Saturday to have struck one of Russia’s largest oil refineries in a drone attack, starting a fire at the facility more than 700 miles into Russian territory.

Fiber-optic drones are highly dangerous, as they can't be jammed with traditional electronic warfare and are difficult to detect.

Russian troops launched 94 drones at Ukraine on the night of January 12. The air defense forces shot down two of them, according to the Air Forces of the Armed Forces of Ukraine. On the night of January 12,