Russia and Ukraine discussed further prisoner swaps on Wednesday at a brief session of peace talks in Istanbul, but the sides remained far apart on ceasefire terms and a possible meeting of their leaders.

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.

Deaths have been reported on either side of the border, just hours after a third round of ceasefire talks took place in Turkey.