IN CONFLICT, physical changes often happen quickly: a road is closed, an apartment block flattened. Mental changes, meanwhile, happen slowly and imperceptibly. It has taken a long time for the realisation to sink in that Ukraine's “crisis” is really a war, and quite possibly a long one. “Too much blood has been spilled to speak of peace,” says ‘Dushman’, a senior rebel commander in Donetsk. When this correspondent first met Dushman last spring, he spoke of how to keep Ukraine united, and called himself Ukrainian. Now Dushman keeps Ukrainians as prisoners. “We took nine yesterday,” he says with a grin.

With separatist forces again on the offensive, eastern Ukraine is taking ever darker turns. Nine months of battle and 5,000 deaths have only fueled the spread of cynicism and hate. One recent rebel propaganda video shows a commander called “Givi” forcing captured Ukrainian soldiers to eat their insignia. The Kiev authorities, in turn, have done little to dispel the perception, common among many civilians inside rebel-held territory, that they want to “destroy the people of Donbas”. A new set of restrictions for crossing the de facto border seem more punitive than protective. Convoys carrying humanitarian aid, including medicine, to Donetsk and Luhansk have been blocked by Ukrainian battalions, drawing condemnation from Amnesty International.

The fighting is picking up momentum along the entire front. On January 24th a barrage of rockets struck civilian neighbourhoods on the eastern edge of Mariupol, a strategic Ukrainian port city, killing 30 and wounding scores. One senior Ukrainian official described it as “genocide”. Alexander Zakharchenko, the Donetsk rebel leader, told an emotional crowd that the attack on Mariupol was “the best possible monument to all our dead”. Russia blamed Kiev for the deaths; hours after his first statement, a chastened Mr Zakharchenko walked back his bluster on Russian television. But analysis of the impact craters by experts from Human Rights Watch and the Organisation for Security and Co-operation in Europe suggests the rockets were fired from rebel-held areas.

The shelling of Mariupol puts added pressure on the West to respond to the rebel push, one that NATO now says is backed by Russian troops. Many in the West hoped that sanctions, the falling oil price and international isolation would coax Vladimir Putin into a compromise. Instead, further violence in Ukraine has become a “means of blackmail” for Mr Putin, argues Lilia Shevtsova of the Brookings Institution. The West has found itself in a corner of its own: inaction now would amount to capitulation, while action means engaging in a fight few want. In order to protect its credibility, “The West will be forced to take a step that even yesterday it was not ready for,” Ms Shevtsova writes.

A “deeply concerned” President Obama has promised to consider all measures “short of military confrontation”. New sanctions seem likely, though America will have to cajole an already hesitant European Union. (European unity will be further tested by the victory in Greece of Syriza, whose leader has spoken out against sanctions on Russia.) Ukrainian officials have begun lobbying to cut Russia off from the SWIFT banking system. But the chairman of a Russian state bank has warned that such a move would bring Russia and the West to the brink of war: “The next day, the Russian and American ambassadors would have to leave the capitals.”

President Obama could also choose to begin supplying Ukraine with defensive weapons, a power recently granted to him by Congress. Many American commentators, including recent ambassadors to Russia and Ukraine, argue that supplying arms would strengthen Ukraine and raise the costs of Russian aggression. But sending weapons may do more to inflame tensions than calm them. Nothing so far suggests Mr Putin will blink.

The Kremlin sees an existential battle with America playing out on Ukrainian soil. Mr Putin has called Ukraine’s army a “NATO foreign legion” fighting for Western interests; images of American weapons being unloaded in Kiev would be taken as proof. Sergei Karaganov, a Kremlin advisor and a dean at Moscow’s Higher School of Economics, argues that the survival not just of the ruling regime, but of Russia itself, is at stake: “This raises the bets much higher than those of Western partners.” And with the Donbas rumbling, Russia’s other neighbours are taking note. Belarus’s newest military doctrine warns of little green men; Lithuania recently issued its citizens a Russian invasion survival manual.

In Ukraine, the Minsk peace accords look like an illusion. The question is no longer whether the war will continue, but how long it will last. “To live means to fight,” says Andriy Biletsky, a commander of Ukraine's Azov battalion, which leads the defence of Mariupol. Over oily pork and potatoes at Dushman's base in Donetsk, one rebel soldier predicts the war will last until 2018. His comrades nod in approval. Asked whether he is ready, Dushman answers: “We have no choice. We have no exit.”