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

Russian strikes killed at least 12 people in Ukraine overnight into Sunday, officials said, as Kyiv and Moscow traded fire amid an ongoing major prisoner swap. Ukraine’s emergency services described a night of “terror” as Russia launched a second straight night of major airstrikes on Ukraine,

Russia and Ukraine each exchanged 307 of their service personnel on Saturday on the second day of a prisoner exchange that, when completed, is set to be the largest such swap in the three-year war between the two countries.