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.

Russia launched a major attack on the Ukrainian capital Kyiv and killed at least 13 people in strikes across the country as the two sides released hundreds more prisoners on the second day of a major prisoner exchange.