When the Ukrainian army recaptured Kherson three weeks ago, there seemed some prospect of the war moving into a final phase that could end with sufficient Russian retreats to make some kind of negotiated settlement possible.

But the mood has since changed, with increasing insistence from Ukraine that all territory taken by Russia since 2015 be returned, including Crimea. This would require such a degree of capitulation that Vladimir Putin might seriously threaten an escalation to weapons of mass destruction.

This makes it unlikely that talks will get under way any time soon - but there are other paths of war available as winter encroaches, and one recent development may mark the start of one in particular.

After Russia's withdrawal from Kherson, the assumption was that the Kremlin would organise its frontline troops into defensive positions, dig in for the winter months and begin the process of preparing for a spring offensive next March. Instead, it has opted for a substantial offensive operation, mainly around the town of Bakhmut in the Donetsk oblast.

The Russian army has had substantial forces deployed there since May, but they have had limited progress in making gains, with a high rate of casualties. Yet in recent weeks, especially since the loss of Kherson, substantial reinforcements have been sent in, leading to some of the most intense ground warfare of the whole war.

A determined and continual onslaught by the Russian forces has been met with a rigorous Ukrainian defence - the result being high casualties on both sides.

A US press report described the scene during a day of fighting earlier this week: "For almost an hour, the stream of Ukrainian casualties in the eastern city of Bakhmut seemed unending: ambulances, an armoured personnel carrier and private vehicles all screamed to a halt, one after another, and disgorged the wounded in front of the city's only military hospital."

That the Russian forces have very little to show for their efforts and burgeoning losses has not deterred them. Why they continue is unclear, with the Institute for the Study of War writing: "Russian efforts around Bakhmut indicate that Russian forces have fundamentally failed to learn from previous high-casualty campaigns concentrated on objectives of limited operational or strategic significance."

One explanation is that there are internal rivalries within the Russian military, with a powerful faction determined to take Bakhmut come what may, probably under heavy pressure from Putin and his people to get results. This may explain the deployment of mercenaries from the Wagner Group - a Russian private military company - to this area, given that the group's founder, Yevgeny Prigozhin, is believed to have leadership ambitions.

Whatever the reason, Putin clearly intends to keep on with the war even though it is proving extraordinarily costly, shown not only by the number of people being killed or maimed but also by the sheer quantity of military materiel used.

In the summer, for example, the Ukrainian army was firing up to 7,000 artillery rounds every day, while the Russians were using over 40,000, and a similar intensity may be evident now. The Ukrainian army has 350 modern Western artillery pieces, but a third of them are out of service at any one time, often because the barrels need replacing.

A problem for Ukraine is that most Western armies scaled down their stocks of weapons after the end of the Cold War, with the largest producer, the United States, making only 15,000 artillery rounds a month. Now, the US and many NATO allies are scrambling to increase their supplies, which will prove highly profitable to arms companies across the West. Sweden, for example, has a new centre-right government that is increasing military spending by close to 90% over the next seven years.

A NATO summit in Bucharest this week agreed to increase weapons supplies and put substantial aid into helping Ukraine repair its critical infrastructure in the face of repeated Russian missile attacks. NATO's direct military aid to Ukraine has already exceeded $40bn this year, close to France's entire annual spending on its military.

This does not mean that Ukraine will get what it wants to win the war, especially since its wish list includes Army Tactical Missile System (ATACMS) surface-to-surface missiles - which have a much longer range than those currently being used with the High Mobility Artillery Rocket System (HIMARS).

But Ukraine may get a proposed new missile being cobbled together from existing components by Boeing, which will have a longer range than those currently being used with HIMARS but a shorter range than ATACMS. It will probably also be provided with necessary anti-missile forces for use against armed drones and cruise missiles.

What would really tip the balance of the war in Ukraine's favour is much longer-range rockets and cruise missiles, able to travel 700 kilometres or more (even ATACMS can travel only up to 300 kilometres). These would be able to hit air bases well inside Russia, which are used by attacking bombers and also for launching missiles.

Washington is cautious about what it supplies to Kyiv, however strong the urging, and it looks as if there are three reasons for this.

One is the risk of advanced technologies getting into expert Russian hands and perhaps being shared with Iran. Another is the fear of pushing Putin to escalate, since NATO directly enabling Ukraine to attack Russia would certainly give him the motive. The third is the view - uncomfortably common in some right-wing and strategic studies circles in the US - that it is best for the war to continue for years if necessary, weakening Russia as a potential threat to long-term US interests, especially if it limits the capacity of a future Sino-Russian axis.

In a previous column, I wrote that talks in the next three months were unlikely unless Putin was under serious pressure - and the determined Russian offensives around Bakhmut are significant in this context.

These offensives suggest that Putin still thinks the Western commitment to Ukraine can be undermined, helped by energy shortages and economic problems across much of Europe. If that is right, then the war could last as a low-level conflict for years to come.

Internal opposition and regime change in Moscow is still possible. In any case, NATO - under US influence - may move to adopt a two-track policy, with increased civil aid for Ukraine and heavy support for its defensive capabilities. This would be aimed at maximising Russian casualties on the ground and further damaging the Russian economy, without Ukraine being able to take the war to Russia itself. All the killing would be in Ukraine. It might be a brutal but effective strategy for hobbling Russia as a long-term threat, but the price paid by Ukraine and its people would be huge.

It took the Taliban two decades to wear down Western armies and force them to retreat, so as a form of warfare it is hardly new.

From openDemocracy