Russia has just ten to 14 more days of full fighting capacity in Ukraine meaning the invasion could soon grind to a halt, according to UK defence sources.
Vladimir Putin 's forces would then start struggling to hold the ground they have already captured from Ukraine, the senior source said, claiming that Kyiv has Moscow "on the run".
Russian soldiers have started to buckle under the pressure of Ukraine's resistance to the invasion which was expected to end in days but is now entering its third week.
Up to 13,500 Russian troops have been killed, scores of aircrafts shot down and tanks and helicopters destroyed, according to Ukrainian reports.
"It is running out of manpower and running out of energy. As long as we keep pressing, they've got ten to 14 days before reaching their culminating point," the UK defence source told MailOnline.
Want all the latest news and analysis from Ukraine? Sign up to our World News Bulletin here
“That's when the strength of Ukraine's resistance should become greater than Russia's attacking force," they added.
Putin has called on other countries for help including China and North Korea, some reports suggest.
However, a spokesperson for the embassy of China denied knowledge of his plea while North Korea allegedly responded "you are too insane for us," according to the author of XSoviet-News Sarah Hurst on Twitter.
This has not been verified by other sources.
Follow the latest updates from Ukraine in our live blog
Now the Russian army could be just two weeks away from "culmination point" while advances across Ukraine have already stopped.
President Volodymyr Zelensky echoed that message in an early morning speech to his people.
The Ukrainian leader said that his army continues to inflict "devastating losses" on Russian soldiers and that soon the number of fallen Russian helicopters will reach the hundreds with 80 warplanes already wiped out.
"Hundreds of tanks and thousands of other units of equipment," he added.
"In 19 days, the Russian army has lost more in Ukraine than in two bloody and years-long wars in Chechnya."
But Russia's method of attack has become more brutal as the invasion is questioned, with cities facing more indiscriminate rocket fire.
Ukraine's capital of Kyiv suffered more bombings on Tuesday when apartment blocks caught fire in early morning strikes with the number of casualties unclear.
Retired General Ben Hodges, former commanding officer of the US Army in Europe, told MSNBC of Russia's decision to transition to "a war of attrition."
He said: “They’re smashing cities, putting civilians on the road because of fear of being murdered.
"They need three things to do this and they don’t have those three things – they don’t have the time, they don’t have the manpower, and I don’t think they have the ammunition.
"That means they won’t be able to continue the attack."
The retired general called on The West to speed up the delivery of Ukrainians' capabilities and destroy Russian long-range artillery, rocket launchers and missile sites.
“It’s kind of a race, actually," he continued.
"If we give the Ukrainians enough, where they can outlast Russia until Russia culminates, then in my assessment, unless something dramatically different happens, it’s about 10 days.”
Putin might turn to 'plan B' – non-conventional weapons – as the invasion of Ukraine falters, a leading Russian journalist has said.
Kremlin troops have continued to bombard civilians in the besieged cities of Kharkiv and Mariupol with further casualties in Kyiv overnight.
An estimated 3m people have fled Ukraine since the invasion on February 24.
