In their call, Downing Street said the two leaders discussed Operation Interflex, which has seen more than 45,000 Ukrainian personnel trained on British soil since Russia invaded Ukraine.

The pair “agreed on the importance of refining its offer to further bolster Ukraine’s ability on the battlefield”, a No 10 spokeswoman said.

“What happens in Ukraine in the coming weeks and months matters to Europe and NATO, and it was vital President Putin’s ambitions fail in Ukraine, the leaders agreed,” she added.

In a post on X, Zelensky said he had thanked Sir Keir and the British people “for their unwavering support that continues to save Ukrainian lives”.

The call came after Sir Keir attended a summit of the Joint Expeditionary Force in Estonia, where leaders discussed support for Ukraine.

The defence coalition is made up of the UK, Denmark, Estonia, Latvia, Lithuania, the Netherlands, Norway, Finland, Sweden and Iceland.

Downing Street said the group “underscored the importance of matching their words with concrete action”, including further sanctions on the “shadow fleet” of ships used by Russia to export oil, the acceleration of lethal aid and support for the Ukrainian defence industrial base.