It comes as Ukraine is celebrating its independence day on Sunday, which marks the country's declaration of independence from the Soviet Union in 1991. The United Nations' International Atomic Energy Agency (IAEA) has repeatedly called on both Russia and Ukraine to show maximum restraint around nuclear facilities in the war.

Many of the drones aren’t particularly fast or high-tech, but they are cheap enough for the Kremlin to launch more than 700 in one night, in an effort to overwhelm Ukraine’s air defenses. Here’s what we know.