UK Prime Minister Rishi Sunak had a phone conversation with Ukrainian President Volodymyr Zelensky on Saturday, during which he told him that London would send Kiev 12 Challenger 2 tanks.

"The Prime Minister outlined the UK’s ambition to intensify our support to Ukraine, including through the provision of Challenger 2 tanks and additional artillery systems," Sunak's office said.

Sunak and Zelensky also agreed on "the need to seize on this moment with an acceleration of global military and diplomatic support to Ukraine," in particular, welcoming Poland and other countries' commitment to start sending tanks to Kiev.

Read: Western armored vehicles to Ukraine: breakthrough or stepback?

Earlier in the day, the Sun newspaper reported, citing sources in the UK government, that out of 12 tanks pledged by Sunak, four would be sent immediately and eight shortly afterward.  

Meanwhile, the Russian Embassy in London said that the decision to send modern samples of heavy armor to Kiev was made "to persuade other, less belligerent Western countries to follow suit and provide their own tanks to the Ukrainian armed forces."

"As for the Challenger 2 tanks, they will hardly help the Ukrainian military turn the tide in the field. Yet they will become legitimate large-scale targets for the Russian forces," the statement read.  

Read: Ukrainian soldiers could be preparing chemical attack: Russian embassy

Ukraine has raised fears of an alleged anticipated Russian attack in the spring, prompting its Western allies to commit to supplying Kiev with heavier weapons, including modern Western-made tanks, which were never part of earlier arms aid packages.

Late last year, The Telegraph newspaper reported that the United Kingdom intended to increase defense spending by around 1.5 billion pounds ($1.8 billion) in light of the Ukraine war. UK Chancellor of the Exchequer Jeremy Hunt is expected to announce the increase for the fiscal year 2025 in the spring of 2023.

In late November, British Prime Minister Rishi Sunak vowed that his country would stand by Kiev's side "until Ukraine has won" during his first visit to the Ukrainian capital since taking office.

The Chief of the General Staff of the Russian Armed Forces, Valery Gerasimov, revealed in December that the West had supplied more than 350 tanks, 700 artillery systems, 100 multiple launch rocket systems, 30 helicopters, at least 5,000 drones, and 1,000 armored fighting vehicles to Ukraine since the start of Ukraine war.

Total foreign financial assistance to Ukraine amounted to almost $100 billion, Gerasimov added.