Russia’s aggression in Ukraine acquired a new dimension with the British Prime Minister warning of a long war. Indeed, Mr Johnson and the head of Nato have called for sustained support for Ukraine as Russia has intensified its assault on the eastern regions.

The separate warnings from Mr Johnson and Mr Jens Stoltenberg on Saturday came as Ukraine’s President Volodymyr Zelenskyy visited front lines in the southern regions of Mykolaiv and Odesa, where he declared  that Ukrainians “will definitely” win against invading Russian troops.

Mr Johnson, writing in The Sunday Times, called for sustained support for Ukraine, saying the country’s foreign backers should hold their nerve to ensure it has “the strategic endurance to survive and eventually prevail”.

The British leader wrote in the 1,000-word article posted online on Saturday night: “Time is now the vital factor. Everything will depend on whether Ukraine can strengthen its ability to defend its soil faster than Russia can renew its capacity to attack. Our task is to enlist time on Ukraine’s side.”

He outlined a four-point plan for “constant funding and technical help”, levels of which should be maintained for “years to come” and potentially be increased. And economic concerns ~ amid global food and energy crises made worse by the conflict ~ should not lead to a rushed settlement in Ukraine, said Mr Johnson, who is battling inflation at 40-year highs  at home and spiraling domestic fuel prices. He added that allowing Russian President Vladimir Putin to keep territory in Ukraine would not lead to a more peaceful world.

“Such a travesty would be the greatest victory for aggression in Europe since the Second World War,” he said. Mr Stoltenberg also appealed for continued support for Ukraine, telling Germany’s media that the supply of state-of-the-art weaponry to Ukrainian troops would increase the chance of liberating the eastern Donbas region from Russian control.

“We must prepare for the fact that it could take years.We must not let up in supporting Ukraine,” he said. “Even if the costs are high, not only for military support, also because of rising energy and food prices.” The presentations by Johnson and Stoltenberg are arguably the most forthright yet by the western bloc over the past four months, indeed ever since Russia invaded the former Soviet satellite.

But it is not certain that the sentiments are shared by other Europeans. On Ukraine’s battlefields, the Ukrainian military reported intensified Russian attacks on its positions in the eastern cities of Kharkiv, Izyum, and Severodonetsk.

It said Severodonetsk, a prime target in Moscow’s offensive to seize full control of the eastern region of  Luhansk in the Donbas region, was again under heavy artillery and rocket fire, but said that the Russian push to establish full control over the city remains “unsuccessful”. However, it admitted that its forces had suffered a military setback in the nearby settlement of Metolkine.