Ukraine has achieved the “functional defeat” of Vladimir Putin’s prized Black Sea fleet with intensified attacks in recent weeks, a UK defence minister has suggested – but warned that Western allies are running out of ammunition to help Kyiv repel Russia’s invasion.

Speaking at the Warsaw Security Forum from the Polish capital on Tuesday, James Heappey said the kneecapping of the major Russian naval force – including the recent strike on its Crimean headquarters – was “every bit as important” as Ukraine’s gains in Kharkiv last year.

While “nobody can pretend otherwise” that Ukraine’s counteroffensive has progressed slowly, the UK’s armed forces minister told delegates it was “simply wrong” to suggest there has been no progress at all – with gains “every single day” after breaching Russia’s “enormous defensive belt and minefield”.

But comparing Kyiv’s relatively minor gains to those achieved last year “diminishes the importance of what has happened in the Black Sea over the last couple of weeks, where a Russian submarine and a Russian ship have been put out of action, and the headquarters of the Black Sea fleet has been put out of action too”, he said.

“The functional defeat of the Black Sea fleet – and I would argue that is what it is, because it has been forced to disperse to ports from which it cannot have an effect on Ukraine – is an enormous credit. And [it is] every bit as important – every bit as much progress – as what was happening in the Kharkiv Oblast last year.”

The Black Sea fleet, of huge symbolic value to Russia, has been an increasing target of Ukrainian drone attacks in recent weeks. Throughout the war, the fleet has been used to launch missile attacks on Ukraine and to threaten Kyiv’s vital shipped grain exports.

With Russia finally pulling out of a UN-brokered grain deal in July, Kyiv has since sought to establish a new corridor hugging the coastline, through which two Marshall Islands and Cameroon-flagged vessels were said to be the lastest ships to sail to the port of Odesa on Tuesday.

And the UK’s Ministry of Defence said on Monday that the Black Sea fleet was “[struggling] to deal with concurrent threats”, with Russia resorting to using air power to “project force” over the area as fleet activies relocate from under-fire Sevastopol to Novorssiysk, some 322km (200 miles) east.

But Mr Heappey and Nato’s most senior military official, Admiral Rob Bauer, were among those to warn that Kyiv’s allies are running out of ammunition, with the latter lamenting that “the bottom of the barrel is now visible” and urging nations to “ramp up production in a much higher tempo”.

“We need large volumes,” the admiral said. “The just-in-time, just-enough economy we built together in 30 years in our liberal economies is fine for a lot of things – but not the armed forces when there is a war ongoing.”

Also warning that Western stockpiles are “looking a bit thin”, Mr Heappey said: “If it’s not the time when there is a war in Europe to spend 2 per cent on defence, then when is?”

Underscoring such warnings, US president Joe Biden – who is struggling to pass a package of aid for Ukraine through Congress – convened a phone call of G7 and Nato leaders on Tuesday in which he expressed determination to secure the funding, with Rishi Sunak also vowing to support Kyiv for “as long as it takes”.

The comments came as Ukraine’s airforce claimed to have destroyed 29 of 31 drones launched by Russia and one cruise missile, most of them targeting the regions of Mykolaiv and Dnipropetrovsk in the south and east, in an overnight barrage of attacks lasting three hours.

With counteroffensive operations continuing in Zaporizhzhia and near Bakhmut, president Volodymyr Zelensky also visited troops and commanders in the northeast near Kupiansk, where the Ukrainian military says Russian forces have also been staging attacks.

Meanwhile, a report alleged that hundreds of drunk, insubordinate and mutinous Russian soldiers have been pressed into penal units known as “Storm-Z” squads and sent to the frontlines as punishment for their behaviour.

“If the commandants catch anyone with the smell of alcohol on their breath, then they immediately send them to the Storm squads,” one soldier told a Reuters investigation, which cited 13 people with knowledge of the matter, including five fighters in such units.