• Ukraine's relations with Germany have soured this week, with Kyiv asking Berlin why it had reversed a decision to provide heavy weaponry to Ukraine, as it had earlier promised.
• Tensions over Germany's provision of promised Leopard tanks and infantry fighting vehicles to Ukraine — or more precisely, the lack thereof — came to a head this week.
• Ukraine's foreign minister, Dmytro Kuleba, publicly asked why Berlin was backtracking on a pledge made to send these weapons to Ukraine.

Ukraine's relations with Germany have soured this week, with Kyiv asking why Berlin reneged on its promise to provide heavy weaponry.

Tensions over Germany's provision of Leopard tanks and infantry fighting vehicles to Ukraine — or lack thereof — came to a head this week when Ukraine's foreign minister, Dmytro Kuleba, publicly asked why Berlin was backtracking on a pledge made to send these weapons to Ukraine.

"Disappointing signals from Germany while Ukraine needs Leopards and Marders now — to liberate people and save them from genocide," Kuleba said on Twitter, adding that there was "not a single rational argument on why these weapons can not be supplied, only abstract fears and excuses."

"What is Berlin afraid of that Kyiv is not?" he added.

The Marder is a German infantry fighting vehicle designed to be used alongside Leopard battle tanks in combat.

Kuleba's comments came as Ukraine launches counterattacks against Russian forces in both the south and northeast of the country. Ukraine's counterattack in the northeast Kharkiv region was hailed as a particular success, with Russian forces withdrawing from towns and villages across the region, almost completely deoccupying it.

Ukraine is largely reliant on Western weapons systems to fight Russian forces. And its allies in the West, NATO members essentially, have individually sent Ukraine a vast range of military hardware.

In April, Germany promised to give Leopard tanks and Marders to Ukraine. Rather than deliver them directly, it proposed a swap scheme. The intention was that NATO members, Poland or Slovakia for example, could send Ukraine older Soviet-era tanks (such as Leopard 1s), and Germany would then replenish their stocks with its own more modern equivalent weapons (such as Leopard 2s).

Germany justified the proposal to send older weapons by saying that Ukraine's forces were used to Soviet-era weapons, and that it should only supply weapons they know how to use.

The only problem with the plan is that this exchange of weapons has largely failed to materialize and Germany is now facing a backlash from critics, both within Germany and externally — and not least of all, from a disappointed Ukraine.

Yuriy Sak, an advisor to Ukraine's defense minister, Oleksii Reznikov, told CNBC on Wednesday that Kyiv doesn't understand Berlin's reluctance to send it weapons that could prove decisive on the battlefield.

"It's difficult to read their minds, but Germany's words, during the last seven months on a number of occasions, have not been matched by their actions. And this is disappointing because there was a moment in time when they made this commitment that they would provide Ukraine with these tanks, it was a moment of hope and promise that we looked forward to," he noted.

"If they're afraid of some nuclear strikes or some other attacks on the nuclear power plant in Zaporizhzhia, which could result in major tragedy, it's another story but as far as the situation on the battlefield is concerned, we don't understand the logic behind it. It could be some internal political games as well," he noted.

Kyiv wants weapons, Germany has them

Ukraine's need for more weapons comes as the war enters what could be a definitive phase in which the balance shifts in Kyiv's favor.

Russia was seen to have been taken by surprise by Ukraine's latest counterattacks, having redeployed some of its most effective fighting units to southern Ukraine after Kyiv signaled over the summer it would launch a counteroffensive to retake Kherson.

After what seemed like a brief period of stunned silence as it took in Ukraine's rapid victories and advances in the northeast, Russian forces have begun their response to those wins, launching an intense series of attacks on energy infrastructure in the northeast, as well as missile strikes on the south.

All the while, Ukrainian President Volodymyr Zelenskyy has called on Ukraine's international allies to continue sending weapons, saying this is when it needs them most to maintain the momentum.

And it's weapons like Germany's Leopard tanks, and Marder infantry fighting vehicles, that Ukraine says could change the balance of the war definitively.

Among Ukraine's NATO allies, Germany — the self-professed "leader of Europe" — has attracted criticism and even ridicule for its military assistance to Ukraine. Just before Russia launched its invasion on Feb. 24, Germany's offer to send thousands of helmets to Ukraine was met with derision.

Analysts say that criticism is not entirely deserved, however, noting that after the U.S. and U.K., Germany has been one of the biggest donors of weapons to Ukraine.

Stijn Mitzer and Joost Oliemans run a Dutch open-source intelligence defense analysis website and keep a tally of weapons Germany has delivered to Ukraine.

They note on their site that, to date, these deliveries include a number of Gepard SPAAGs (self-propelled anti-aircraft guns), man-portable air defense systems (known as MANPADS, they're portable surface-to-air missiles), howitzers, and anti-tank weapons, as well as hundreds of vehicles and millions of rounds of ammunition. The German government has also published a list of the military equipment it has sent to Ukraine, right down to 125 pairs of binoculars it has donated.

But when it comes to German tanks and infantry fighting vehicles, Germany has ostensibly dragged its feet, with no decision on the supply of such hardware, let alone deliveries, made despite Ukraine's specific requests from Kuleba and other officials since March. Analysts say Germany's good intentions have just not come to fruition.

"Germany has ... attempted to entice other countries to send their heavy weaponry to Ukraine in a programme known as 'Ringtausch' ('exchange'). Under this policy, countries can receive German armament free of charge in exchange for delivering tanks and infantry fighting vehicles from own stocks to Ukraine," Mitzer and Oliemans noted in an article in early September.

"Although a promising scheme at first, the 'Ringtausch' programme has largely failed to live up to expectations as most countries expect to have their Soviet-era systems replaced by larger numbers of modern weapon systems than what Berlin is currently able (or willing) to offer," they noted.

What does Germany say?

Pressure has been mounting on German Chancellor Olaf Scholz to make a decision on sending such weapons to Ukraine, but there appears to be reluctance at the top to take that decision. On Monday, Germany's defense minister, Christine Lambrecht, said sending more heavy weaponry to Ukraine was "not so simple."

"It's not so simple just to say: I'll just risk that we won't be able to act, the defense of the country, by giving everything away. No, I won't do that," she said. "But we have other possibilities, from industry, with our partners," Deutsche Welle reported.

CNBC contacted the German Defense Ministry for more comment, and a response to Kuleba's comments, and is yet to receive a response.

Scholz defended Germany's record over weapons deliveries on Wednesday, however, telling reporters that "it can be said that the very weapons that Germany has now provided to Ukraine are decisive to the development of the conflict in eastern Ukraine, and they have also made the difference" in battle.

Germany's reticence over certain arms deliveries has prompted some critics to look for ulterior motives for its reluctance, with some even suggesting that Germany does not like the idea of German tanks facing Russian tanks on the battlefield, as they did in World War II.

Rafael Loss, a defense expert at the European Council on Foreign Relations, told CNBC Wednesday that the German government has put forward various explanations for not sending the weapons.

"The German government itself has put forward explanations for why not to do so, essentially, since the beginning of Russia's war against Ukraine and even before that. We've heard concerns about the potential for escalation, that Russia might see the transfer of such weapons as some kind of red line."

"We see concerns, mostly from the SPD (Scholz's Social Democratic Party) about the images that German Leopard tanks might produce going toe to toe with Russian tanks in Ukraine. And we've also heard in the past arguments about the tight timeline as a reason for sending the Soviet-produced materiel first. I think that that is a legitimate argument. But it only holds up so long," he said.

"At some point, Ukraine — and the countries that will be able to support Ukraine with these types of systems — will run out of them, and you can't replace them as easily. So at some point, you need to start thinking about Western supply chains that are based on Western western systems."

Loss characterized Germany's stance toward Ukraine as one of "immense" resistance to sending weapons unilaterally, and that it would prefer some kind of European coalition that jointly sends arms and assistance.

"Over the past six or four months, we've seen an immense reluctance both from the Chancellery and from the Defense Ministry to be proactive, to take the initiative and they've always referred to 'not going it alone,'" Loss said, adding that Germany appeared to want the U.S. to take the lead and for Berlin to follow.

Ukraine left waiting

While the pressure is mounting on Berlin to act, Germany's stance is unlikely to change anytime soon, or potentially at all, according to Anna-Carina Hamker, a Europe researcher at political risk analysis firm Eurasia Group. She said in a note Wednesday that Scholz's government — a coalition of his Social Democratic Party, Greens and pro-business Free Democrats, uncomfortable bedfellows at the best of times — would likely continue to struggle over its Ukraine policy.

"Major adjustments to the government's Ukraine policy are unlikely and the coalition will not significantly step up arms deliveries, despite Ukraine's territorial gains over the last few days," she said in a note.

As such, Ukraine has been left fuming and disappointed by Germany's stance, leaving Kyiv to question Berlin's commitment to supporting it as the war continues into the fall and likely the winter, unless there is a dramatic change of course from the Kremlin.

Ukrainian Defense Ministry official Yuri Sak summed up Kyiv's frustrations toward Germany, noting that "one of the arguments is that they are afraid of further escalation — but that's an invalid argument because it's like, an escalation to what? It's bad enough as it is."