Ukrainian President Volodymyr Zelensky has accused Russia's Vladimir Putin of sabotaging diplomacy over his response to the US-Ukrainian proposal for an unconditional 30-day ceasefire.
"He is now doing everything he can to sabotage diplomacy by setting extremely difficult and unacceptable conditions right from the start even before a ceasefire," Mr Zelensky said in a post on X.
Mr Zelensky also said that he saw a good chance to end the war with Russia, after Ukraine and the US proposed a 30-day ceasefire, to which Moscow said it would only agree if certain conditions were met.
He said the Russian president would try to drag the ceasefire proposal into endless discussions, and urged the US and Ukraine's other allies to apply pressure on Russia.
Meanwhile, US President Donald Trump has urged Mr Putin to spare Ukrainian troops being pushed back out of Russia's Kursk region and said there was a "very good chance" the war could end.
Mr Trump posted on social media after his envoy, Steve Witkoff, held a lengthy meeting with Mr Putin on last night in Moscow that Mr Trump described as "very good and productive."
"There is a very good chance that this horrible, bloody war can finally come to an end," he said.
The US president said thousands of Ukrainian troops were "completely surrounded" by the Russian military and "in a very bad and vulnerable position."
"I have strongly requested to President Putin that their lives be spared. This would be a horrible massacre, one not seen since World War II. God bless them all!"
Military analysts have said Ukrainian forces in Kurskare nearly cut off after rapidly losing ground in what had been their only foothold in Russian territory.
However, Ukraine's military immediately said there was no threat of encirclement, and that troops were pulling back to better positions.
White House press secretary Karoline Leavitt said that Mr Trump himself had not spoken to Mr Putin yet.
Read more: Zelensky slams Putin's 'very manipulative' statements on ceasefire
The Kremlin said Mr Putin had sent Mr Trump a message about his ceasefire plan, which Ukraine has agreed to, via Mr Witkoff, expressing "cautious optimism" that a deal could be reached to end the three-year-old conflict.
The US President wants to see a swift ceasefire in a conflict that he says has the potential to spiral into World War III.
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Trump urges Putin to sign ceasefire deal with Ukraine
Mr Trump again pressed Russia to sign and complete "a Cease Fire and Final Agreement", saying on his private social media platform that he would extract the US from what he called a "real 'mess' with Russia".
Mr Putin said yesterday that he supported Mr Trump's proposal in principle, but that fighting could not be paused until several crucial conditions were worked out, raising the prospect of longer negotiations.
Despite its heavily qualified nature, Mr Trump called Mr Putin's statement "very promising".
Kremlin spokesman Dmitry Peskov said that Mr Putin - who has expressed concern that Ukraine would exploit any truce to regroup - had used the late-night meeting with Mr Witkoff to convey information and "signals" to Mr Trump.
"There are certainly reasons to be cautiously optimistic," Mr Peskov said.
"(Putin) said that he supports President Trump's position in terms of a settlement, but he voiced some questions that need to be answered together".
Mr Peskov said the timing of a phone call between the presidents would be worked out once Mr Witkoff had briefed Mr Trump.
Mr Putin has said he wants Ukraine to drop its ambitions to join NATO, Russia to control the entirety of the four Ukrainian regions it has claimed as its own, and the size of the Ukrainian army to be limited.
He has also made clear he wants Western sanctions eased and a presidential election to be held in Ukraine, which Kyiv says is premature while martial law remains in force.
Mr Peskov played down US media reports suggesting Russian officials had told US counterparts they did not want Mr Trump's Russia-Ukraine envoy Keith Kellogg to be involved in top-level discussions on the war.
He said Russia had no intention of meddling.
