Ukrainian resistance has put the Russian army "on the run" and a growing shortage of resources means they won't be able to keep up the fight for more than two weeks, it is claimed.
Russia has failed to make the big inroads it is thought they were expecting and are making slow progress in trying to topple the Ukraine regime in Kyiv.
They are slowly encircling the Ukraine capital but it is thought now that the inability to make decisive blows means that they will run out of "manpower and energy" sooner rather than later.
Now, a senior UK defence source is reported to have said that "Ukraine has Russia on the run" and the attacker was running out of both manpower and energy.
The source told the Daily Mail: "As long as we keep pressing they've got 10 to 14 days before reaching their culminating point. That's when the strength of Ukraine's resistance should become greater than Russia's attacking force."
A similar view to the Mail source, where Russia will be forced to call a halt to their invasion by May, was held by Oleksiy Arestovich, an adviser to the Ukrainian president's chief of staff, speaking late on Monday.
In a video published by Ukrainian media, Arestovich said the exact timing of a withdrawal would depend on how much resources the Kremlin was willing to commit to the campaign.
"I think that no later than in May, early May, we should have a peace agreement, maybe much earlier, we will see, I am talking about the latest possible dates," Arestovich said.
"We are at a fork in the road now: there will either be a peace deal struck very quickly, within a week or two, with troop withdrawal and everything, or there will be an attempt to scrape together some, say, Syrians for a round two and, when we grind them too, an agreement by mid-April or late April."
A "completely crazy" scenario could also involve Russia sending fresh conscripts after a month of training, he said.
Still, even once peace is agreed, small tactical clashes could remain possible for a year, according to Arestovich, although Ukraine insists on the complete removal of Russian troops from its territory.
The war in Ukraine began on February 24 when Vladimir Putin launched what he called a "special military operation," the biggest attack on a European state since World War Two.
Ukrainian President Volodymyr Zelensky gave a nightly address where he talked of the Russian forces suffering "devastating" losses and he tried to get their soldiers to surrender.
"Therefore, I offer you a choice. On behalf of the Ukrainian people, I give you a chance. Chance to survive," he said.
"If you surrender to our forces, we will treat you the way people are supposed to be treated. As people, decently. In a way you were not treated in your army. And in a way your army does not treat ours. Choose!
"Our brave defenders continue to inflict devastating losses on Russian troops. Soon the number of downed helicopters of Russia will reach hundreds of units. They have already lost 80 warplanes. Hundreds of tanks and thousands of other units of equipment.
"In 19 days, the Russian army has lost more in Ukraine than in two bloody and years-long wars in Chechnya. For what?"
