File image: Ukrainian servicemen are seen along the frontline in Donbas, Ukraine earlier this month. Photo:
In a keynote speech in London, UK Foreign Secretary Liz Truss said victory for Ukraine was now a "strategic imperative" for the West.
It amounts to the clearest statement yet of Britain's war aims which have, until now, been limited to stating that President Putin's invasion of Ukraine "must fail and be seen to fail".
She said Western allies must "double down" in their support for Ukraine.
"We will keep going further and faster," Truss said, "to push Russia out of the whole of Ukraine."
This implies that Russian forces must leave not just the territory occupied in recent weeks since their invasion on 24 February but also those areas they invaded and annexed eight years ago, such as Crimea in the south and parts of the eastern Donbas region.
A month into this latest invasion, Russia declared its main goal was the "liberation of Donbas" - broadly referring to Ukraine's regions of Luhansk and Donetsk.
More than a third of this area was already seized by Russian proxy forces in a war that began in 2014.
Not all Western powers may share Truss' ambitious target, fearing it is unlikely to be achieved either by arms or negotiation.
Some French and German officials have been more cautious about stating war aims that risk provoking Russia, preferring to focus instead on language about defending Ukraine.
The foreign secretary's latest remarks in a speech at Mansion House in London reflect the desire by some in the West to aim high, so that Ukraine enters any possible future talks about a political settlement to the conflict with the best negotiating hand possible.
Truss also used her speech to make clear the West should do more to deter future Russian aggression.
This, she said, should include more spending on defending itself, with the Nato target of spending 2 percent of national output on defence seen as "a floor not a ceiling".
UK Foreign Secretary Liz Truss Photo:
'Untold misery'
She also said Western powers should use their "economic heft" to exclude Russia from western markets.
"Access to the global economy must depend on playing by the rules," she said.
But Labour's shadow foreign secretary David Lammy said earlier on Wednesday that the speech "appears to be an admission of failure after more than a decade of decline" in the government's commitment to defence and security.
Truss also set out her view that the West should send weapons to other countries threatened by Russia.
"We must ensure that, alongside Ukraine, the Western Balkans and countries like Moldova and Georgia have the resilience and the capabilities to maintain their sovereignty and freedom."
She added that if Sweden or Finland chose to join Nato, "we must integrate them as soon as possible".
She said: "The war in Ukraine is our war - it is everyone's war because Ukraine's victory is a strategic imperative for all of us.
"Heavy weapons, tanks, aeroplanes - digging deep into our inventories, ramping up production. We need to do all of this."
"We cannot be complacent - the fate of Ukraine remains in the balance. And let's be clear - if Putin succeeds there will be untold further misery across Europe and terrible consequences across the globe."
Russia's president Vladimir Putin warned earlier on Wednesday that any country meddling in Ukraine would be met with a "lightning" fast response.
"We have all the tools [to respond] that no one can boast of," he told Russian lawmakers. "And we will not be bragging about them, we will use them if necessary."
- BBC