reassurance

But given the president's previous ambivalence about Nato, alliance members want reassurance that when the sovereignty of an ally is threatened, Washington can be relied on to respond.

“It would serve as a testament to his judgment in choosing me and reassurance that if something happened, the country was in good hands. My success was important for him.”

Earlier this week, Putin rejected Western proposals for a "reassurance force" in Ukraine the day after any ceasefire comes into place, following a Paris summit aimed at finalising plans for security guarantees.

And this came just a day after Kyiv's allies, the so-called Coalition of the Willing, had pledged a post-war "reassurance force" for Ukraine.

"It's much more about European security, this adjustment with America, the reassurance to America that Europe is taking more responsibility for its security. The energising of Europe," Sir Tony said.