Russian President Vladimir Putin expressed support for a U.S. ceasefire proposal to halt Russia’s war with Ukraine for 30 days, but he stressed that many details would have to be worked out and that any truce should pave the way to lasting peace.

“We agree with the proposals to halt the fighting, but we proceed from the assumption that the ceasefire should lead to lasting peace and remove the root causes of the crisis,” Putin told reporters Thursday in Moscow. He went on to list several issues he said needed clarifying.

Ukrainian President Volodymyr Zelenskyy said that Putin’s comments were “very manipulative” and that he thought Putin’s qualified support for the U.S. plan was an effort to ultimately lay the groundwork for rejecting it, according to Agence France-Presse.

“He is in fact preparing a rejection at present, because Putin is of course scared to tell President [Donald] Trump that he wants to continue this war, that he wants to kill Ukrainians,” Zelenskyy said in his evening address, according to Reuters.

At the White House, Trump said it would be “very disappointing” if Russia rejected U.S. efforts to end the fighting.

“We would like to see a ceasefire from Russia,” Trump told reporters. “A lot of the details of a final agreement have actually been discussed. Now we're going to see if Russia is there and, if not, it will be a very disappointing moment for the world."

Earlier, Putin’s top foreign policy aide dismissed the United States’ 30-day ceasefire proposal, saying it would merely provide Ukraine’s military with a temporary respite from fighting.

His comments came after U.S. special envoy Steve Witkoff arrived in Moscow to meet with Russian officials on the ceasefire proposal. In his comments, Russian presidential aide Yuri Ushakov confirmed he has been in regular contact with U.S. national security adviser Mike Waltz and said they agreed these contacts would remain confidential.

U.S. officials met earlier this week with Ukrainian officials in Saudi Arabia to present the ceasefire plan.

Ukrainian President Volodymyr Zelenskyy welcomed the U.S. effort, saying Wednesday that Ukraine is “ready for a ceasefire for 30 days as proposed by the American side.”

Zelenskyy said the halt in fighting could be used to create a broader peace deal for the conflict, which began with Russia’s February 2022 full-scale invasion of Ukraine.

Zelenskyy said a ceasefire would provide time “to prepare answers to all questions regarding long-term security and a real, reliable peace and put on the table a plan to end the war.”

Zelenskyy’s chief of staff, Andriy Yermak, meanwhile, said on Thursday that Ukraine would not agree to a frozen conflict with Russia.

“We said very clearly that we will never agree to a frozen conflict,” Yermak said on television, according to Reuters, referring to discussions between Ukraine and the United States in Jeddah. He added that the U.S. was also against a frozen conflict.

The talks in Moscow between the U.S. and Russia come as the Russian Defense Ministry said Thursday that its forces had retaken control of Sudzha, a major town in Russia's western Kursk region, from Ukrainian troops.

Ukrainian forces took the town during a surprise attack on the Kursk region bordering Ukraine last August and had been struggling to hold it ever since.