Russia launched its largest aerial assault of its three-year war on Ukraine overnight, targeting the capital and other regions with missiles and drones for a second night in a row, even as the two sides prepared to conclude a major prisoner exchange.

Russia and Ukraine exchanged hundreds more prisoners Saturday as part of a major swap that amounted to a rare moment of cooperation in otherwise failed efforts to reach a ceasefire.

The attack involved nearly 370 missiles and drones, according to Ukraine’s Air Force. At least 12 people were killed.