Boris Johnson is to hold discussions with Ukraine’s president Volodymyr Zelenskiy in a visit to the country on Tuesday.
The prime minister, who will be accompanied by foreign secretary Liz Truss, will promise to “uphold Ukraine’s sovereignty” amid mounting tensions with Russia.
But he may turn up without having spoken to Vladimir Putin after the domestic scandal over illegal parties forced him to reschedule a planned phone call with the Russian leader.
The tele-meeting had originally been scheduled for Monday afternoon but as the evening the Kremlin was unable to offer Mr Johnson another spot in Mr Putin’s diary.
Mr Johnson was too busy on the domestic front dealing with the fallout from the Sue Gray inquiry to honour the original planned time.
As news of the PM’s trip to Ukraine emerged prime minister also faced speculation and criticism that he was fleeing the country to escape bad news about lockdown rule breaking.
Ahead of the meeting, Mr Johnson said: “It is the right of every Ukrainian to determine how they are governed. As a friend and a democratic partner, the UK will continue to uphold Ukraine’s sovereignty in the face of those who seek to destroy it.
“We urge Russia to step back and engage in dialogue to find a diplomatic resolution and avoid further bloodshed.”
Russia has placed around 100,000 troops near Ukraine’s border but denies it has plans to invade the country.
The PM has previously said the UK could deploy troops to protect Nato allies if Russia invades Ukraine.
Ukraine is however not a part of Nato, and Russia wants the alliance to promise it will never be allowed to join.
Russia views Nato as a threat to its security and is concerned about increasing Western influence over Ukraine, which it was in political and economic union with until the 1990s.
But Ukraine’s leaders say its future lies in closer ties with Western Europe and that it should be able to choose its own destiny.
Russia annexed Ukraine’s Crimean peninsula in 2014 and has backed rebels who have seized large parts of the eastern Donbas region.