The announcement appears to preclude any kind of top-level meeting or breakthrough ahead of the 50-day deadline for an agreement given by President Donald Trump.

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 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.