The warring sides remain far apart after the third round of U.S.-brokered peace negotiations on Wednesday. But there was progress on humanitarian issues.

Ukraine and Russia attacked targets on each other's territory on Thursday after brief direct talks between the two sides failed to make any progress on steps to end nearly three-and-a-half years of war.

Officials from Russia and Ukraine ended a third round of formal negotiations in Istanbul with an agreement to swap more prisoners but little sign of progress on a deal to halt the war.