Russia and Ukraine have agreed to exchange 1,000 prisoners of war from each side following the first direct talks between the two warring countries in three years.
Under pressure from President Donald Trump to end the conflict, delegates from both countries met for the first time since March 2022, the month after Russia invaded its neighbour.
The talks in an Istanbul palace lasted well under two hours, and there was no immediate announcement on whether or when the sides might meet again.
Russia expressed satisfaction with the talks and both countries said they had agreed to exchange 1,000 prisoners of war from each side.
But Kyiv, which wants the West to impose tighter sanctions unless Moscow accepts a proposal from Trump for a 30-day ceasefire, immediately began rallying its allies for tougher action.
As soon as the talks ended, President Volodymyr Zelensky held a phone call with Trump and the leaders of France, Germany and Poland, his spokesperson said.
Russia's demands were "detached from reality and go far beyond anything that was previously discussed," a source in the Ukrainian delegation told Reuters.
The source, speaking on condition of anonymity, said Moscow had issued ultimatums for Ukraine to withdraw from parts of its own territory in order to obtain a ceasefire "and other non-starters and non-constructive conditions".
Prime Minister Keir Starmer said the Russian position was unacceptable and that European leaders, Ukraine and the US were "closely aligning" their responses.
Zelensky said robust sanctions should follow if Russia rejected a ceasefire.
Expectations for a major breakthrough, already low, were dented further on Thursday when Trump, winding up a Middle East tour, said there would be no movement without a meeting between himself and Russia's President Vladimir Putin.
Turkish Foreign Minister Hakan Fidan said Ukrainian and Russian officials had agreed in principle to meet again for negotiations aimed at reaching a ceasefire.
