Yet Russia and Ukraine are still battling for the small city of Bakhmut.

After nearly eight months of trench warfare, Ukrainian forces are surrounded on three sides, Kyiv's supply lines are fraying, and Moscow is in control of just under half of Bakhmut.

Still, Ukraine has pledged to double down on the city's defence even as both sides take heavy casualties.

Some leading Western military analysts have suggested it might make sense for Ukrainian forces to fall back to a new fortified defensive line, but Kyiv shows no sign of doing that for now.

Military commanders said their own counteroffensive — backed by newly delivered Western hardware, including German Leopard 2 tanks — was not far off but stressed the importance of holding Bakhmut in the meantime.

So what makes the city so important, and what's the state of play in the longest and bloodiest fight of the war so far?

Reminiscent of World War I, the battle for Bakhmut has been fought from trenches with relentless artillery and rocket strikes across a heavily mined battlefield described as a "meat grinder" by commanders on both sides.

It has also involved house-to-house fighting.

'Fortress Bakhmut' getting 'hot':

Ukrainian President Volodymyr Zelenskyy has portrayed "Fortress Bakhmut" as a symbol of defiance that is bleeding the Russian military dry.

For Moscow, the fall of the city it calls by its Soviet-era name of Artyomovsk would be its first major capture since mid-2022 and a boost in its wider war against Ukraine.

On Sunday, Mr Zelenskyy said the military situation was "especially hot" around the city.

A senior Ukrainian official had earlier described the situation around the town as "tense", with the military command carefully considering every move.

The comments came as the founder of Russia's Wagner mercenary force, Yevgeny Prigozhin, said his troops had raised a Russian flag on the administrative building in the city.

But there was no indication from Ukrainian officials that Bakhmut had fallen into Russian hands.

City becomes killing zone:

Images of battlefields strewn with corpses from both sides have surfaced on social media, and Mr Prigozhin has published a picture of his own dead fighters.

Casualty figures are classified, but US officials estimated that tens of thousands of Russian soldiers — many of them convicts recruited by Wagner — have been killed.

Thousands of Ukrainian troops are believed to have died too.

Mr Zelenskyy's aide, Mykhailo Podolyak, said Ukraine was fighting in Bakhmut because the battle was pinning Russia's best units and degrading them ahead of a planned Ukrainian spring counteroffensive.

Konrad Muzyka, a Polish military analyst who recently visited the Bakhmut area with colleagues, said he thought it no longer made military sense to hold the city.

"The decision to defend Bakhmut is now a political one, not a military one," Mr Muzyka told Reuters, saying the scale and the costs of Ukrainian losses now outweighed the benefits of holding the city from a military point of view.

Psychological boosts:

For Russia, Bakhmut would be a morale-boosting battlefield win after a string of defeats last year.

For Ukraine, the loss of Bakhmut could sap morale, even if — as its allies say — it might not make much of a strategic difference.

Both Pentagon chief Lloyd Austin and NATO head Jens Stoltenberg have played down the potential fall of Bakhmut as symbolic, as have Western military experts.

In a sign of Bakhmut's importance for Kyiv, Mr Zelenskyy presented the US Congress with a battle flag signed by the city's defenders when he visited the United States in December.

Retaining the city helps sustain support from Western countries, proving it is making a difference, according to Michael Kofman, an expert on the Russian military at the US-based CAN think-tank.

If the city does fall, Ukraine could take comfort from the fact that it held off Russian forces for so long and extracted such a high price for Bakhmut, suggesting any Russian attempt to take more territory would be similarly costly.

Sources | Reuters / ABC