US Secretary of State Marco Rubio has said he expected Russia to present a Ukraine ceasefire outline within days that will show if it is serious, as Moscow rejected Ukrainian and European accusations it was trying to drag out the peace process.
Russia's rebuttal came after Ukrainian President Volodymyr Zelensky accused Moscow of buying time.
US President Donald Trump spoke separately by telephone on Monday to Mr Zelensky and Russian President Vladimir Putin, after Russian and Ukrainian officials met in Istanbul on Friday for their first direct talks on the conflict in three years.
Mr Putin has consistently rejected proposals for a 30-day truce put forward by Ukraine and its Western allies.
But Mr Rubio said Mr Putin and Russian Foreign Minister Sergei Lavrov indicated they would present their own terms "maybe in a number of days, maybe this week hopefully".
Russia will offer "just broad terms that would allow us to move towards a ceasefire, and that ceasefire would then allow us to enter into detailed negotiations to bring about an end of the conflict," Mr Rubio said.
He said the presentation will "tell us a lot about their true intentions".
"If it's a term sheet that's realistic and you can work off of it, that's one thing. If it makes demands that we know are unrealistic, I think that will be indicative," he added.
Italy's Prime Minister Giorgia Meloni said Pope Leo XIV was willing "to host upcoming discussions between the parties at the Vatican," according to her office.
US President Donald Trump said "it would be great" for Russia and Ukraine to hold ceasefire talks at the Vatican, saying it would add extra significance to the proceedings.
But Russia said no decision had yet been made on a venue for talks when asked if they could be hosted by the Vatican.
Kremlin spokesperson Dmitry Peskov said Russia welcomed "the readiness and efforts of all parties who want to contribute to a speedy settlement", but nothing had been decided yet about where the next meeting should be held.
Russia had not received any specific proposals from the Vatican, he said.
Mr Rubio insisted that Mr Putin "hasn't gotten a single concession" from Mr Trump. But Russia has also not indicated any new flexibility since Mr Trump took office in January with vows to end the war through dialogue.
Mr Putin after Mr Trump's call said he was ready to work with Ukraine on a "memorandum" outlining a possible roadmap and different positions on ending the war, prompting new accusations from Kyiv and European governments that Moscow was stalling and had no serious interest in peace.
Mr Peskov rejected the claims, saying "nobody is interested in delaying the process".
"Everyone is working dynamically. We will keep you informed. Of course, most of this work is being done in a discreet mode, and it should not, for obvious reasons, be open to the public," he added.
His remark followed a social media post by the Ukrainian president in which he said it is "obvious that Russia is trying to buy time in order to continue its war and occupation".
Jeanne Shaheen, the top Democrat on the Senate Foreign Relations Committee, told Mr Rubio that Mr Putin's refusal to go to Istanbul despite the stated willingness of both Mr Zelensky and Mr Trump to meet showed "he believes it's in Russia's interest to carry out this war as long as possible".
Yesterday, the European Union formally adopted its 17th round of sanctions on Russia, targeting 200 vessels of Russia's so-called shadow maritime fleet.
Kirill Dmitriev, the head of Russia's Direct Investment Fund and lead economic negotiator with the US, attacked the move, saying "Western politicians and the media are making titanic efforts to disrupt the constructive dialogue between Russia and the United States".
Mr Rubio said that Mr Trump for now opposed new sanctions for fear that Russia would no longer come to the table.
Russia appears confident, with its troops advancing on the battlefield and Mr Trump ending Western isolation of the Kremlin.
The memorandum mentioned by Mr Putin "buys time for Russia," Russian political analyst Konstantin Kalachev said.
"The cessation of hostilities is not a condition for it, which means that Russia can continue its offensive," he added.
The warring sides met in Istanbul last week for their first face-to-face negotiations since March 2022 and agreed a swap of 1,000 prisoners on each side, but Russia did not agree to an immediate, unconditional ceasefire that Ukraine was seeking.
Russia invaded Ukraine in February 2022 and has since destroyed swathes of the country's east, killed tens of thousands and now controls around one-fifth of its territory.
