Putin no longer able to recruit Russian troops quickly enough to replace those dying on battlefield

However, armed forces minister Al Carns insisted that the depletion of Russia's number of fighting men did not mean the UK could relax its commitment to raise defence spending.

The Government has announced Britain will provide new military, energy and humanitarian support to Ukraine, as Sir Keir Starmer is set to convene a coalition of the willing meeting alongside French President Emmanuel Macron.

Between 30,000 and 35,000 Russian soldiers are recruited each month, according to western officials.

But the number of those killed over the past three months is believed to have been higher than those who joined up.

This means that for the first time in the four years of war, for a sustained period, Moscow's battlefield numbers are falling. Russia invaded Ukraine on February 24 2022.

Mr Carns described this as a "casualty uptick which is disproportionate in scale".

Western officials believe this will have a significant impact on the Kremlin's ability to "generate offensive power" for a spring or summer offensive, meaning that any Russian forward march would be sluggish.

It also raises the prospect of "coercive" mobilisation within Russia, such as conscription, rather than relying on the promise of large financial rewards to recruit soldiers.

Drone attacks continue to be the driving force behind the casualty rate on the battlefield, and officials believe that ground-based drones - so-called unmanned ground vehicles (UGVs) - will become ever more present over the coming year.

However, Mr Carns said individual soldiers remain "essential" for capturing and holding ground once drone attacks are over.

The minister was also asked by reporters why there was still a need to continue to increasing UK defence spending, given messaging from officials about Russia's falling battlefield numbers.

Britain has promised to spend 3.5% of national income on defence by 2035, which it made in line with a pledge by Nato members last year.

Mr Carns insisted it was important to "not confuse the two", adding: "Russia is taking huge casualties on the front line, but we've also got to think to other domains.

"For example, cyber has cost us £15 billion alone to the economy. We've seen a 50% uptick in hostile state attacks just on the MoD (Ministry of Defence) alone."

As the full-scale war in Ukraine enters its fifth year, the Government has announced a new package of support aimed at bolstering Kyiv's war effort.

This includes a £20 million package to help repair and protect the nation's power grid - often a target of Russian strikes - as well as £5.7 million assistance for Ukrainians whose towns and villages are on the front line of the war.

Ukrainian military medics are also being mentored by British surgeons, nurses and physiotherapists in battlefield surgery.

Sir Keir will convene a virtual meeting of the coalition of the willing to discuss recent peace talks and further support for Kyiv amid the ongoing conflict.

Foreign Secretary Yvette Cooper will spend Tuesday in Kyiv, where she will call out "Russification" tactics being used by Moscow in occupied Ukrainian territories.

People in the territories are being forced to adopt Russian passports, are prohibited from speaking the Ukrainian language and are arrested on arbitrary charges for expressing pro-Ukraine sentiments, according to the Foreign Office.

The Prime Minister said: "On this grim anniversary, our message to the Ukrainian people is simple: Britain is with you, stronger than ever. That is why we are announcing new support today and we will continue to support Ukraine for as long as it takes.

"For all the noise in world affairs today, this war remains the most critical issue of our age.

"It asks the question of whether Ukrainian and European freedom will endure.

"Our answer, together, is unequivocal: Russia is not winning this war. They will not win this war.

"Ukraine's courage continues to hold the line for our shared values, in the face of Putin's aggression.

"We will stand by their side, until a just and lasting peace - and beyond. Slava Ukraini."

Russia's bombardment of Ukraine continued over the weekend, with a barrage of missiles and drones killing one person in Kyiv and striking the country's energy grid.

Ukrainian officials have meanwhile said that the next round of talks aimed at ending the war could come as early as the end of this week.

The country's president, Volodymyr Zelensky, has told reporters he believes Mr Putin started a third world war with the invasion of Ukraine.

"I believe that Putin has already started it. The question is how much territory he will be able to seize and how to stop him... Russia wants to impose on the world a different way of life and change the lives people have chosen for themselves," he told the broadcaster.