A G7 meeting to commemorate the anniversary of Russia's invasion will feature Rishi Sunak urging allies to "move faster" in arming Ukraine.
Giving Ukraine a "decisive" advantage in the conflict "must be our priority now," the prime minister will say during a video call on Friday.
No. 10 promised to argue for the provision of the nation with longer-range weapons.
The call will occur on a day when commemorations will be held for the war's first anniversary.
At 11 o'clock GMT, there will be a moment of silence in the UK, and Mr. Sunak will host Ukrainian troops at a Downing Street event.
Labour leader Sir Keir Starmer will call for the UK to "double down" on support for Ukraine as other British political figures observe the anniversary.
According to the US military, at least 100,000 soldiers from each side have been killed or injured in the conflict, which started when Russia invaded Ukraine on February 24 of last year.
Along with the more than 13 million people who have been displaced within Ukraine or abroad, thousands of civilians have also been killed.
As Russia prepares for an anticipated spring offensive, Ukraine has urged its Western backers to step up their assistance.
Mr. Sunak is anticipated to state during the virtual summit of the G7 leaders that "shifting Putin's mindset will require an acceleration of support.".
Now, he will say, "This must be our top priority.". "Instead of taking a step-by-step approach, we need to move more quickly on air defense, armor, and artillery. ".
He is anticipated to argue for giving Ukraine "longer-range weapons" to prevent Russia from attacking Ukraine's infrastructure, something he promised the UK earlier this month.
Volodymyr Zelensky, the president of Ukraine, stepped up his requests to Western countries to give his nation modern fighter jets during a recent tour of Europe.
Ukrainian forces will soon be trained by the UK to operate jets to NATO standards. However, like other Western countries, it hasn't yet provided jets, claiming that doing so would only be a long-term solution.
The main political parties in the UK have united in their support for Ukraine, but Mr. Sunak has come under pressure from some of his own Conservative MPs to provide fast jets as soon as possible.
Using the anniversary to reiterate his call for President Zelensky to be given weapons "to finish the job," former prime minister Boris Johnson, who was in office when Russia invaded, is among those calling for quicker action on jets.
In a statement made available to journalists, he said, "The past year has taught us that sooner or later, the West gives the Ukrainians what they need.
For the benefit of Ukraine and the rest of the world, let's make that decision sooner if it is the only option. ".
In commemoration of the occasion, Sir Keir urged UK political parties to maintain their current level of cooperation in the coming months.
"Putin's barbaric invasion has been doomed to failure," he declared, citing the bravery and tenacity of the Ukrainian people and the support of their allies around the globe.
"We should be motivated by their strength and determination to intensify our support for them.
Their struggle against tyranny for democracy, freedom, and liberty is also our struggle.
The leader of the Liberal Democrats, Sir Ed Davey, praised the "amazing acts of bravery in Ukraine" and pledged that the UK would "stand in solidarity with Ukraine until they achieve victory.".
Scottish First Minister and SNP leader Nicola Sturgeon expressed her wishes for a "speedy victory for Ukraine" in a letter to Ukrainians living in Scotland in honor of the anniversary.
