At a G7 gathering to commemorate the anniversary of Russia's invasion, Rishi Sunak is expected to urge allies to "move faster" in arming Ukraine.
The prime minister will say in a video call on Friday that giving Ukraine a "decisive" advantage in the conflict "must be our priority now.".
No. 10 promised to argue for the provision of longer-range weapons for the nation.
The call will occur on a day when commemorative activities will mark one year since the war started.
At 11:00 GMT, there will be a minute of silence in the UK, and Mr. Sunak will host Ukrainian troops at an event on Downing Street.
The anniversary will be observed by other British political figures, with Labour leader Sir Keir Starmer urging the UK to "double down" on its support for Ukraine.
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, according to the US military.
Over 13 million people have been forced to flee their homes in Ukraine or abroad, and thousands of civilians have also been killed.
As Russia prepares for what is expected to be a spring offensive, Ukraine has been pleading with its Western backers to increase their assistance.
Mr. Sunak is anticipated to state that "shifting Putin's mindset" will require an acceleration of support during the virtual summit of the G7 group of advanced economies.
He will add, "This must be our top priority right now. "Instead of taking a step-by-step approach, we need to advance artillery, armor, and air defense more quickly. ".
He is anticipated to argue in favor of providing Ukraine with "longer-range weapons" in order to prevent Russia from being able to target Ukraine's infrastructure, as he promised the UK earlier this month.
Volodymyr Zelensky, the president of Ukraine, stepped up his requests to Western countries to send his country modern fighter jets during a recent tour of Europe.
Ukrainian forces will soon be trained by the UK on Nato jets. But like other Western countries, it hasn't provided jets yet, claiming that doing so is still a long-term possibility.
Although the UK's major political parties have come together in support of Ukraine, Mr. Sunak has come under pressure from some of his own Conservative MPs to provide fast jets as soon as possible.
The anniversary was used by former British Prime Minister Boris Johnson to reiterate his call for President Zelensky to be given weapons "to finish the job." Johnson was in office at the time that Russia invaded, and he is one of 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.".
And if that is the decision, let's make it sooner for the benefit of Ukraine and the rest of the world. ".
As he observed the anniversary, Sir Keir urged UK parties to maintain their current level of cooperation in the coming months.
He said, "Putin's barbaric invasion has been doomed to failure by the resolve and bravery of the Ukrainian people, supported by their allies throughout the world.
"We ought to be motivated by their fortitude and resolve to step up our support for them.
It is also our fight to uphold democracy, freedom, and liberty in the face of tyranny.
Announcing that the UK would "stand in solidarity with Ukraine until they achieve victory," Liberal Democrat leader Sir Ed Davey praised the "amazing acts of heroism in Ukraine.".
SNP leader and Scottish First Minister Nicola Sturgeon wished for a "speedy victory for Ukraine" in a letter she wrote to Ukrainians living in Scotland to commemorate the anniversary.
