They stressed that in strict military terms there had been a withdrawal ordered by Russian defence chiefs in north east Ukraine, rather than an “outright collapse” of troops’ discipline in following their commanders.
“However, the professionalism of how individual units have conducted the withdrawal has varied greatly,” one official added.
“Some have retired in relatively good order.
“Others, including militia of the self-proclaimed Donetsk People’s Republic, have indeed fled in apparent panic.
“In places, a significant quantity of operational vehicles, weapons and ammunition have been abandoned.”
Western nations also agree with Ukrainian reports that around 6,000 square kilometres (2,300 square miles) have been liberated in the Kharkiv area from Russian occupation.
The official added: “Russian forces are likely in the process of withdrawing from the whole of the occupied northern Kharkiv Oblast (province), an area of up to 10,000 square kilometres. (3,800 square miles)”
The official declined to comment on claims that the US or UK played a role in advising on the plans for the Ukrainian counter-offensives in the southern Kherson province and the north east Kharkiv area.
He added: “It’s the Ukrainians fighting, it’s Ukrainian decision-making, these are Ukrainian successes.”
Mr Putin and Moscow were also said to be taking an increasingly “interventionist” approach to the war, which he started on February 24.
“It’s a major limiting factor for the Russians,” the official explained.
“It’s fair to say that we are seeing more signs of Moscow operating with a long screwdriver which is inhibiting the action on the frontline as opposed to the Ukrainians, their decision-making cycle is much, much faster.”
There is now “grassroots dissent in Russia which calls out the decision-making and also Putin for putting Russia into a situation” and “open discussion about the failure of the special military operation,” he added.
But this “growing pressure” within the Russian system is not yet believed to be at a level to threaten the Russian president’s position or his regime.
Ukraine had succeeded in generating an “offensive striking force” to open up a flank at the “operational level”, with its Kharkiv and Kherson advances.
It was too early to say if the recent success of Volodymyr Zelensky’s forces was a turning point in the conflict.
But it is being seen in western capitals as a “moment which has power in terms of both operations, logistics and psychology”.
Ukrainian forces have seized back dozens of villages and towns in the north east ahead of winter, showing they can make gains as Mr Putin seeks to weaken western resolve to support Kyiv by cutting back on gas supplies to many European countries.
Military chiefs in Ukraine had from late July unleashed “multiple threats” against the occupying Russian army, which led to some forces being moved, creating “areas of weaknesses”.
Ukraine had exploited these weaknesses by “concentrating forces” against them, including with the surprise counter-offensive around Kharkiv.
“Clearly, what the Ukrainians have managed to do, with the resources available, is impressive,” said the official.
“They have identified a gap, they have exploited the gap and they have taken it up to a natural boundary where we can see that they are starting to destroy bridges and will now need to consolidate their gains.”
Some Russian command posts are believed to have been captured.
But Russia had made some “good decisions” in giving up territory to withdraw to better defensive lines, to protect its gains in the Luhansk province of the Donbas industrial region.
The forces’ ratio in the southern Kherson region is “finely balanced,” so while Ukraine had made some gains, Russia has the ability to be agile and limit these advances.
But it had not been able to do so in the north east.
The frontline was now “very long”, stretching some 500 miles in a direct line from Kherson to north of Kharkiv.
So the armies on both sides are “stretched”.
The official described Russian forces like “a crust, and as you punch through there are vulnerabilities”.