Ukraine's intelligence service said it also believed Moscow intended to fire an intercontinental ballistic missile later on Sunday as an attempt to intimidate the West. There was no immediate response from Moscow to the accusation.
President Volodymyr Zelenskiy, straining to restore ties with Washington after a disastrous February White House visit, met Vice President JD Vance and Secretary of State Marco Rubio in Rome on Sunday on the sidelines of Pope Leo's inauguration.
Zelenskiy said the meeting was "good" and released pictures of Ukrainian and US officials sitting outside at a round table and smiling. Ukrainian media said the meeting lasted 40 minutes.
"I reaffirmed that Ukraine is ready to be engaged in real diplomacy and underscored the importance of a full and unconditional ceasefire as soon as possible," Zelenskiy said.
Zelenskiy also met Pope Leo following the new pontiff's inaugural Mass at the Vatican.
Ukraine and Russia held their first face-to-face talks in more than three years on Friday, under pressure from Trump to agree to a ceasefire in a war he has pledged to bring to a quick end. The warring sides agreed to swap 1000 prisoners each but failed to agree to a truce, after Moscow presented conditions that a member of Ukraine's delegation called "non-starters".
The leaders of Britain, France, Germany and Poland planned to speak to Trump before the US and Russian presidents speak on Monday, German Chancellor Friedrich Merz said on Sunday.
The four European leaders jointly visited Kyiv last week where they called for new sanctions on Russia unless Moscow accepts a ceasefire, and Zelenskiy has said they joined him in phoning Trump on Friday after the Russia-Ukraine talks.
After a night of air alerts, Ukraine's air force said that as of 8am local time on Sunday Russia had launched 273 drones at Ukrainian cities, more than the previous record Moscow had set in February on the war's third anniversary.
Trump has shifted US rhetoric from supporting Ukraine towards accepting some of Moscow's narrative about the war that Putin launched in 2022. But Kyiv and its European allies are working hard to persuade Trump that it is Moscow that is holding up a truce now.
Zelenskiy has said he would accept Trump's proposal for an immediate ceasefire of at least 30 days with no conditions. Moscow says it would consider a ceasefire but only if conditions are met, including a halt in arms supplies to Kyiv.
It also says any peace talks must address the "root causes" of the conflict, including its demands that Ukraine cede territory, be disarmed and accept neutral status. Kyiv calls that tantamount to capitulation and says it would be left defenceless in the face of future Russian attacks.
On Saturday, a Russian drone attack killed nine civilians after hitting a shuttle bus in the Sumy region in northeastern Ukraine, Kyiv said. Zelenskiy called the attack "deliberate" and urged stronger sanctions on Moscow, which said it had attacked a military facility.
