On 2 May, a fire in the historic city of Odessa in southern Ukraine killed dozens of pro-Russian separatists, increasing fears of an all-out war. At dusk, as pro-Ukraine activists stormed a trade union office occupied by separatists in the city centre, the building was set alight.

It was the bloodiest incident of this conflict so far. People choked to death on smoke or died jumping from windows as they tried to escape the flames. Russian TV aired graphic footage of the fire and its aftermath – charred bodies in pools of blood, including a woman who was reportedly pregnant – relentlessly over the weekend. Many fear that this could give Vladimir Putin, who already claims that Russia might be “forced to act” to “protect” Ukraine’s Russian-speaking population, the pretext he needs to begin an invasion. Others argue that he doesn’t need a pretext; if he wants to invade, he will.

The tragedy came amid mounting violence in the east as the Kyiv government launched its latest counterterrorism operation, the first that has seriously tried to clear pro-Russian separatists from their strongholds. Over the past weeks, the Ukrainian army has advanced steadily towards the occupied cities and fighting between the two sides has intensified.

In the small industrial town of Sloviansk, the centre of the east’s continuing crisis, Ukraine special forces engaged local separatists in hours of heavy gunfire on its northern outskirts on 5 May. Four Ukrainian soldiers and at least 20 separatists were killed. The defence ministry also reported that one of its helicopters had been shot down during the assault – the third to be downed by separatists in a matter of days.

The counterterrorism operation remains confused. Soldiers alternate between intense bouts of violence and long periods of inaction as the Kyiv government alternates between the need to restore order in what is still – barely – a sovereign state and the desire to avoid giving the Kremlin any excuse for further invasion. The army, underfunded and underequipped, also faces the problem of the local population, sections of which form human shields by mingling with the armed militia or gathering around occupied buildings, making it harder for the army to attack.

Back in Kyiv’s Maidan Nezalezhnosti (“Independence Square”), the scene of the February revolution that overthrew the then president, Viktor Yanukovych, the atmosphere has darkened. Maidan is still filled with members of the militia left over from the uprising who have refused to leave until the presidential elections on 25 May. Dressed in camouflage and carrying bats and sticks, they loaf on the streets by day and spend their nights in the tents around the square. Maidan remains cosmetically militarised – ringed by barricades of tyres and sandbags – but it has become little more than a tourist trap, selling souvenirs of the revolution to the trickle of foreigners who still visit.

Now the barricades are being reinforced and expanded. On 5 May, access into the square via a neighbouring street was controlled by a blonde militia girl of no more than 17, who manned a makeshift gate allowing vehicles access in and out. The armoured personnel carrier parked incongruously in the middle of the street – which some of the more enterprising militiamen had been charging people 50 hryvnias a turn to sit in and have their photo taken – was being cleaned and tested.

Both sides are adopting a war mentality, the most obvious – and ominous – aspect of which is the dehumanisation of the enemy. Pro-Russians describe the Odessa fire as “inhumanity . . . last seen by the Nazis in the Second World War”, while the more extreme pro-Ukrainian elements post memes that mock those who died.

A collective psychosis, born of machismo and paranoia and fuelled by rumour, is taking hold. The latest story gaining traction in the capital is that thousands of Russians – solitary males of military age – have begun to appear in Kyiv, renting rooms and just waiting. “Let them come,” says Maksym, my wiry and intense landlord. “I’ve got body armour and I’m cleaning all my guns.”

It is a phenomenon I have seen repeatedly: in Lebanon, in Congo, in Israel. Men sit in the cafés and bars of Kyiv vowing to smash “Putin”. Machine-gun-wielding sep­aratists tell me they will “cleanse” Ukraine of the “fascist junta” in Kyiv. “If the Russians come, I’ll be up there with my Kalashnikov,” an ex-soldier friend tells me, pointing to the gaudily lit roof terrace of my local sushi restaurant.

Many members of the camouflaged militia are unemployed young men from small towns, who have a new purpose and sense of belonging. It’s hard to imagine them willingly returning to their previous lives now.

Whether or not the two sides will face each other in the coming weeks remains to be seen. What is clear is that the further destabilisation of Ukraine is Moscow’s goal, at least in the short term.

Central to Russian propaganda and the arguments of the separatists is that the Kyiv government is an “unelected junta”. By democratically electing a new president, some legitimacy would be restored, which is what Putin fears. One of his spokesmen recently said that it would be “absurd” to proceed with the polls.

Even if the elections do go ahead, the winner is likely to have only a slim mandate. Pro-Russian sympathisers in the east will boycott the elections on principle and it is difficult to see the militants who control the occupied cities allowing the citizens there to vote unmolested.

The two sides are now divided by un­mitigated hate. It is difficult to envisage a future for Ukraine free from further chaos and violence.