European Union leaders meet in Brussels on Saturday, and Nato heads of government in Wales next week, to formulate fresh responses to the dangerously escalating crisis in Ukraine. Their language will be pugilistic, but in truth Vladimir Putin is the only boxer in the ring. He has invented a wholly new type of combat in Ukraine, which has got the west confused and reeling. He dodges blows like Muhammad Ali, one minute claiming he has no control over the separatists, the next (just last night) calling on them to release “encircled” Ukrainian forces. What is he up to? No one knows.

Never in history has an invasion been so “deniable”. According to Moscow, Russian paratroopers found deep inside Ukraine were “lost”; others are “on holiday” there; an armoured column spotted crossing the border did so “by accident”. All this is rather imaginative, compared with the “little green men” who took Crimea in the spring.

Then there was Russia’s humanitarian aid convoy of 260 trucks, which was widely decried in the west as a Trojan horse, “almost certainly” carrying arms and men deep into Ukraine. In fact, it proved to be less a Trojan than a Potemkin horse, half-empty inside and designed to impress – and perhaps to divert attention from the real military subterfuge going on elsewhere. More aid convoys are promised – and the next step could be to provide “peacekeeping” troops to protect them.

The upshot of all this smoke-and-mirrors activity is clear: Russia is stealthily gaining territory, and Putin could be on the verge of annexing another bit of Ukraine, after absorbing Crimea in March.

Redrawing borders, whether by outright invasion or by stealth, is utterly unacceptable. But how can it be stopped? And how can that be done quickly – before the divisions and hatred between Ukrainians and Russians grow so deep that a de facto border emerges between eastern Ukraine and the rest of the country (which might indeed be Putin’s aim)?

Western leaders divide along a spectrum from all-out confrontation (marked by total distrust of Putin) to cautious engagement. Those who see Putin as the only cause of the problem refuse to concede he might also be part of the solution. Those who regard total resistance as the only option dismiss all concessions and even negotiations with Putin as “appeasement”.

All, however, agree on the need for sanctions. And that is the west’s biggest mistake.

Sanctions against Russia have proved, and will always prove, worthless. The relentless desire to continue with them is cockeyed, since they hurt western companies and economies, and are of no avail in changing Putin’s policies. They may well succeed in ruining the Russian economy, but what will that bring? More of the same – or worse. It was the humiliation of Russia and impoverishment of its citizens in the 1990s that brought Putin to power in the first place.

And yet the delusion persists that sanctions can be widened and deepened, strengthened and escalated, until finally Putin caves in. But nothing in his character, or in Russia’s behaviour in the past, suggests this will happen. The only outcome is that time is wasted on an endless search for new targets to punish, instead of grappling with the root causes of the conflict.

Since sanctions don’t work, and war is unthinkable (President Obama on Thursday explicitly ruled out military intervention), then only one viable option remains. If Ukraine is to become peaceful and whole again, and Putin prevented from carving chunks out of neighbouring countries, there needs to be political engagement with Moscow.

There would have to be an immediate, total ceasefire by Kiev and the rebels, followed by talks on a constitutional settlement to protect the rights of the Russian minority. Putin might well be persuaded to back this (and withdraw his phantom forces from Ukraine) if he is promised that Ukraine will never join Nato. The alliance’s leaders could use their Welsh summit to reverse their 2008 declaration that Ukraine “will become” a member. The west could then drop its sanctions, and Russia would end its own retaliatory ban on western imports. Crimea’s annexation would have to be accepted, at least for the moment, for the sake of preserving the rest of Ukraine.

The outcome of the coming week’s deliberations, however, is all too predictable. Further sanctions, more tough talk, an absence of diplomacy, and more deaths and destruction, as the Kiev government tries to bomb the separatists into submission. The end result could be the very thing the west wants to prevent Putin from achieving – the partition of Ukraine.