Vladimir Putin's attack plans will have been hit by up to 14 Russian military helicopters reported to have been destroyed by Ukraine using US-supplied long-range tactical missiles, British defence chiefs said on Friday.
They stressed that it was the first time that these long-range army tactical missiles are believed to have been used in the conflict.
They added that, if confirmed, the losses at two air bases, would also make it harder for Putin's forces to maintain their current defensive lines.
In its latest intelligence update, the Ministry of Defence in London said: “On 17 October 2023, several Russian helicopters and air defence equipment were likely struck at Berdyansk and Luhansk airfields.
“Although the extent of damage is currently unconfirmed, it is likely nine Russian military helicopters at Berdyansk and five at Luhansk were destroyed, with Ukraine claiming to have used the US-provided long-range army tactical missiles (ATACMS) for the first time.”
The briefing added: “Given that Russian fixed wing close air support to date has been extremely poor, Russian defensive lines have become increasingly reliant on rotary wing support in the face of the Ukrainian offensive.
“Berdyansk was being used as a primary Forward Operating Base on the southern axis providing both logistics and offensive/defensive capabilities.
“If confirmed, it is highly likely these losses will have an impact on Russia’s ability both to defend and conduct further offensive activity on this axis.”
The British military chiefs believe that Russia’s military will struggle to replace the lost aircraft in the “short to medium term” given limits on its production, and that this will put more pressure on its existing fleet “already almost certainly suffering combat exhaustion and maintenance issues” given that the war is dragging on far longer than Putin expected.
Russian commanders may be forced to relocate operating bases and command and control centres farther from the front lines, they added, increasing the burden on logistics chains.
Britain, the US, Ukraine and its other allies are fighting an information war against Russia so their briefings need to be treated with caution, but are far more believable than the propaganda issued by the Kremlin.
Meanwhile, Ukraine President Volodymyr Zelensky said he has spoken by phone with US President Joe Biden about Washington's future support for Kyiv, with Britain stressing backing will not be hit by the Middle East crisis.
Mr Biden has compared Putin's invasion to the slaughter by Hamas in Israel of more than 1,400 people and vowed neither would succeed, seeking billions more dollars for America to back its allies.
The contact between the US president and Mr Zelensky came as Putin visited a military base near the Ukrainian border, as the warring countries laid plans for combat operations over winter and the coming year.
Almost 20 months of war have sapped both sides' military resources. The fighting is likely to settle into positional and attritional warfare during the approaching wintry weather, analysts say, with little change along the more than 600-mile front line.
Mr Zelensky said late on Thursday he spoke to Mr Biden about "a significant support package" for Ukraine. Western help has been crucial for Ukraine's war effort.
Putin visited the headquarters of Russia's Southern Military District, less than 60 miles from Ukraine's south-eastern border, where he was briefed on the war by the chief of the General Staff, Valery Gerasimov, the Kremlin said.
With uncertainty over the scale of Kyiv's future Western aid, and after Ukraine's five-month counter-offensive sapped Russian reserves but apparently only dented Russian front-line defences, the two sides are scrambling to replenish their stockpiles for 2024.
Ukraine has been expending ammunition at a rate of more than 200,000 rounds per month, according to Jack Watling, a senior research fellow at the Royal United Services Institute think tank in London.
Mr Watling wrote in an assessment: "Sufficient ammunition to sustain this rate of fire is not going to be forthcoming as Nato stockpiles deplete, and production rates for ammunition remain too low to meet this level of demand."
Meanwhile, Russian production "has turned a corner", he said. Moscow's domestic ammunition production is growing quickly, at more than 100 long-range missiles a month compared with 40 a month a year ago, for example, according to Mr Watling.
Also, Russia is reported to be receiving supplies from Iran, North Korea and other countries.
Though Ukraine's counter-offensive has not made dramatic progress against Russia's formidable defences, it has suppressed the Kremlin's forces and Kyiv is looking to keep up the pressure.
That will help stretch Russia's manpower resources which are already under strain, according to the Institute for the Study of War, a Washington think tank.
It said in its latest assessment that "Russian forces largely lack high-quality reserves and are struggling to generate, train and soundly deploy reserves to effectively plug holes in the front line and pursue offensive operations".
