ISTANBUL (Reuters) -The first high-level talks between Russia and Ukraine since the early months of Moscow's 2022 invasion showed they are far from agreement on steps needed for a ceasefire, even though they promised a major swap of prisoners of war. A window for more diplomacy remains ajar, however, after the sworn enemies agreed in principle to hold further talks, the foreign minister of host country Turkey said, a crucial point for U.S. President Donald Trump, who wants a rapid peace. The negotiators' promises to release a thousand prisoners of war, to meet again for talks and to present their vision for a ceasefire were "substantial steps", said Peter Slezkine, a senior fellow and director of the Russia program at the Stimson Center.