Lt Col. Kaarel Mäesalu, of the EDF's general staff, added that estimates on how much ammunition Russian forces have used is harder to pin down, telling ERR that: "If we take S-300 series missiles, the Ukrainians say the Russians have about 8,000, whereas other sources put the figure at 23,000."

"They've certainly used up a lot, though I believe they still have a few left. I somehow don't think the Russians are so stupid as to use their entire arsenal up."

The S-300 anti-aircraft missile, while designed for aerial targets, has been pressed into use against land-based targets also, Mäesalu said.

"It is interesting that they've started using them specifically for ground targets. They seem to have less ordnance in the 90-150km range, but since there's so and abundance [of the S-300 missiles] they're probably more likely to use them," he went on.

Furthermore, in a situation where the war has transformed into one of long-range missile attacks, Ukrainian forces have been left no alternative but to ask for additional aid from western countries, he went on

"I expect [Ukrainian forces] will still run out of ammunition, because it how much artillery ammunition has been used in this war has amazed many people; the use of ammunition has been intensive in the extreme. Clearly, they do not have an infinite supply."

"Mostly their ammunition production levels are quite modest also; the ammunition made available from the Russians (ie. captured from Russian forces – ed.) during the course of this conflict has been chaotic, it cannot be planned for in advance, while [the Ukrainians] have also stated several times in public that they want to exchange their weapons for western ones, because the western production remains at full strength, plus in this way they would also get ammunition for these weapons," Mäesalu continued.

Those weapons Ukraine has received form the West have arrived rapidly, but are of a wide range in variety which, he said, was not ideal from the perspective of maintenance.

"Each weapon system requires its own unique spares, and its own maintenance methods. Given that the Ukrainians were trained very rapidly to use these weapons, my assessment is that they were probably not adequately trained to maintain them, from crew level onward to higher level repair and maintenance," Lt Col. Mäesalu went on.

Of reports that Russian forces have been sent from the Kherson region, where they have been in retreat since the Ukrainian liberation, to the eastern Donetsk region, Mäesalu said that this likely arose from concerns over losing this territory, along with the Luhansk Oblast, first occupied by Russian or pro-Russian forces in 2014.

"If they lose these, it would be a represent a major strategic communication problem for the Russians domestically, as well. Maybe that's why they want to relocated the center of gravity there," Mäesalu said.

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