KYIV (Reuters) - Ukraine has discussed ways to pressure Russia into agreeing to a 30-day ceasefire with U.S., French, British and German senior officials, President Volodymyr Zelenskiy's top aide said on Thursday, part of a flurry of diplomacy to try to end the war.

Andriy Yermak, Zelenskiy's chief of staff, did not say when the online talks with U.S. special envoys, Steve Witkoff and Keith Kellogg, France's top diplomatic adviser Emmanuel Bonne, Britain's national security adviser Jonathan Powell and Guenter Sautter, a top adviser to the German leader, took place.

But he said all parties "emphasised that a complete and unconditional ceasefire should be the first step towards a just and sustainable peace".

"We also discussed instruments of pressure in case Russia refuses the initiative or violates the agreements," Yermak said on Telegram.

Ukraine has expressed readiness to accept a U.S. proposal to enact an immediate, interim 30-day ceasefire, which could be extended by mutual agreement of the parties, and has accused the Kremlin of ignoring the plan. Putin has proposed a ceasefire of only three days - from May 8-10.

"The Kremlin's proposal for a three-day truce is not about peace, but about safely holding of the parade in Moscow. This is political manipulation," Yermak said.

Russia, which launched a full-scale invasion of Ukraine in 2022, is preparing to stage a military parade on May 9 to mark the 80th anniversary of the defeat of Nazi Germany in what President Vladimir Putin hopes will be a show of strength.

On Thursday, after the declared ceasefire had come into effect, the skies over Ukraine's major cities were quiet, though there were reports of clashes in eastern Ukraine.

(Reporting by Elizabeth Piper; Editing by Gareth Jones)