Joanna Kikis

Putin says Russia is retaliating for a drone strike the Russians say killed more than 20 people, many of them teenagers.

at a college in Russian-occupied eastern Ukraine.

Ukraine denies targeting the school and says it hit a Russian elite drone unit nearby.

But the Kremlin is also really agitated by Ukraine's use of long-range drones to target the lifeblood of the Russian economy, which is oil.

Ukraine has struck Russian oil refineries and depots as well as ports.