They believe Kyiv’s estimate of needing 300 tanks and 600-700 armoured vehicles as not being an “unreasonable” military mass for such a strike in coming months.
On the prospects of a complex, combined arms manoeuvre in March, one western official said: “Both sides are cognisant of the need to reconstitute their forces and put themselves into a position where they can move from the defensive to the offensive in a meaningful way.
“It’s a race to be able to do that first. That will be meaningful.
“Clearly, both sides are striving to do that, the Ukrainians with western support.”
He stressed that timing of any order to launch a spring offensive, by Vladimir Putin or Volodymyr Zelensky, would also be key.
“The longer you wait, perhaps, the more capable your forces will be, the better trained, the better equipped, and better positioned to go on the offensive,” he explained.
“On the other hand, the longer you wait, the more you might lose the advantage, and things become more static and grinding.
“Both sides have a choice.”
He added: “Since the summer, Russian commanders have clearly obsessed about potential for a really major Ukrainian offensive.
“Based on their preparation of defensive positions, it’s likely they see particular danger of an attack in the Zaporizhzhia region or in Luhansk Oblast (province) where intense fighting is already going west of Kremina.”
A “breakthrough” around Melitopol could severe the link through Ukraine between Russia’s Rostov region and Crimea, he added.
Mr Zelensky has been urging western nations to send tanks, with Britain reportedly considering supplying Challenger II tanks.
Putin’s military chiefs have paused for at least ten days the wave of attacks on key infrastructure in Ukraine including electricity power plants.
Western officials believe that this may be because Moscow lacks the missile and drone supplies to keep up the pace of the strikes which have failed to break the will of the Ukrainian people to oppose Putin’s invasion.
“Ukraine’s people have shown some real resilience,” said one official.
The Russian attacks on infrastructure may resume.
But the western officials believe that ultimately Putin’s commanders will have to go back to the “drawing board”.
“Their strategy has not worked,” the official added.
The frontlines in the war, which was launched in February last year, were said to have remained “largely static” as they have since Putin’s retreat from Kherson in November.
The heaviest fighting is taking place around the town of Bakhmut in the Donetsk province of the eastern Donbas region.
Russian forces have made some “tactical gains” in local assaults in recent days, especially around Soledar.
However, western officials doubt this would mark “substantive progress” in capturing Bakhmut, which in turn would only be a “modest” move in seizing control of the whole of the Donetsk province.
They believe that Putin’s “private army”, the Wagner group, is now no longer playing a “niche” role in the war and instead may account for around a quarter of his military in Ukraine, playing a “central role” in the battles as a “major component of the conflict”.
Wagner commanders are sending tens of thousands of “convict recruits” to the frontline in the Donbas, they added, where they are “poorly supported” and suffering “substantial” casualty rates.