In a video message, NATO Secretary General Jens Stoltenberg said Ukraine was on course to join the alliance, but he also described news of Russian advances as “extremely serious”.

“As we prepare you for that day, NATO will continue to stand with Ukraine,” he said.

Former British prime minister Boris Johnson visited Kyiv on Saturday to meet with Zelensky and renewed his call for Ukraine’s allies to send more weapons.

“They need artillery shells and long-range artillery of all kinds,” Johnson said. “It is ridiculous to argue that giving them weapons is provocative or an escalation.”

Russia’s troops, he added, “are firing 10 times as many shells in some places”.

“How can we look these soldiers in the eye and say we are doing enough?”

Last week, Russian soldiers claimed the Kremlin’s first battlefield victory since May with the capture of the town of Avdiivka, although analysts described it as a Pyrrhic victory because 17,000 Russian soldiers were killed during the takeover of the destroyed town.

In an unusually downbeat assessment of the battlefield, the British Ministry of Defence said the Kremlin had suffered massive losses but had since been able to replenish its army.

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“Russian forces in Ukraine are now larger in number than at the start of the war. It is now able to maintain attacks along the front line and pursue a strategy of attrition,” the British ministry said.

Analysts have said that while Europe has struggled to increase its arms production and US domestic politics has slowed the flow of weapons from Washington, Russia has boosted its own munitions production and made deals with North Korea and Iran that have swelled its arms depots.

In capitals across Europe, thousands of people marched against Russian aggression.

The Telegraph, London