Serbia and Kosovo are close to conflict. Of all things, a dispute over car number plates is threatening the fragile peace won 23 years ago, after a Nato bombing campaign against then-Yugoslavia. For that, Serbs have never truly forgiven the West.

On Sunday night, roads were blockaded by Serbs in northern Kosovo. Their anger was directed at an edict from the Kosovan government requiring Serbs to re-register their cars with Kosovar number plates. Serbs currently use number plates with acronyms of Kosovar cities, just one example of Serbia’s ongoing refusal to accept Kosovan independence. New documentation requirements were also to be imposed on Serbs entering and leaving Kosovo.

Some have claimed that tensions have calmed, but they are only on hold. The laws, originally due to come into effect yesterday, have been pushed back a month. Threats of violence won’t vanish in an instance. While no one was injured, gunshots were heard in various locations on Sunday night.

The Serbian president Aleksandar Vučić has portrayed Kosovo’s new laws as aggressive. He says the number plate changes are an attempt to ‘expel’ Serbs, and says the two countries are heading for a ‘new Storm’ – a reference to a 1995 Croatian counteroffensive against Serbs which the country still sees as ethnic cleansing.

While Kosovo and its western allies have said ‘misinformation’ is being spread about the number plate changes, Serbia claims that Kosovo is unilaterally threatening the peace. That interpretation isn’t without sympathy in the West: a former Trump administration special envoy for Serbia-Kosovo peace negotiations described Kosovo’s tactics as ‘fascist’ ways.

It will only take one flashpoint to make a full-blown crisis out of long-running resentments. On Monday, Serb-majority cities in Kosovo draped banners and posters criticising the failures of negotiations over the past decade. On the other side, Kosovan Albanians flew the flag of the Kosovo Liberation Army, a separatist militia that fought in the Kosovo War, which is branded a terrorist organisation by Serbia.

Can the West avert disaster? Kosovo postponed its new policies following pressure from the US and the EU, while the permanent presence of Nato forces in the region is a check on Serbian aggression: this weekend the Nato mission said it is ‘prepared to intervene if stability is threatened’.

Nato’s presence is crucial, since there remains no satisfactory answer to the Kosovo question. Kosovo’s large non-Serb majority rejects rule from Belgrade, but Serbs refuse to let go of the southern region, as much for historical reasons as for its geopolitical significance. Kosovo has long been a battleground for eastern and western forces: a Serbian Christian folklore surrounding Kosovo has developed in opposition to centuries of Ottoman rule.

Serbia’s stance is only hardening. The EU has long hoped that Serbia would soften its position on Kosovo in exchange for membership, but that bargain would most likely be rejected. Serbian support for EU membership plummeted to less than half this year after the EU said recognition of Kosovo was a precondition of joining (despite the fact that five EU countries – Cyprus, Greece, Romania, Spain and Slovakia – also refuse to recognise Kosovo).

This is a pivotal moment for whether Serbia looks east or west. Belgrade is increasingly dissatisfied with the EU’s calls for it to align more clearly with the bloc, demands which have been hardened by the Russian invasion of Ukraine. Serbia’s stance on the war is ambivalent: the EU’s desire for it to join the sanctions programme have been ignored. Serbia can’t commit to Brussels since Moscow is the one backing its claims on Kosovo. Putin strongly opposed the Nato bombing campaign on Yugoslavia, and saw Kosovo’s subsequent declaration of independence as an outrage. But he recently posed the question: if Kosovo was allowed to break away from Serbia with the West’s support, why can’t Crimea, Donetsk and Luhansk split from Kyiv with the Kremlin’s backing? A Russian foreign ministry spokesperson said Kosovan ‘radicals’ are now ‘taking another step towards the expulsion of the Serbian population’, echoing Putin’s rhetoric on the separatist clashes in the Donbas.

The war in Ukraine is dividing Europe, and risks pulling Serbia further towards the Kremlin. The West must tread carefully. Backing Serbia into a corner could make Belgrade more likely to lash out against Kosovo. The next few months could be dicey, and with long-held resentments threatening to break out into the open, the situation in Kosovo looks less like a question and more like a riddle with no right answer.