Volodymyr Zelenskyy will skip a high-level conference on the postwar reconstruction of Ukraine amid a deepening rift with Poland over his naming of a military unit for one that killed tens of thousands of Poles during the second world war.

Ukraine’s president had been expected to co-host the Ukraine Recovery Conference, which begins in the Polish coastal city of Gdańsk on Thursday, but the Ukrainian delegation will instead be led by the prime minister, Yulia Svyrydenko.

The annual conference, which in previous years took place in Rome, Berlin and London, seeks to bring together partners and businesses that could help with rebuilding Ukraine after the war.

Zelenskyy’s decision not to attend follows weeks of tensions with Poland over his decision last month to name a military unit after “the heroes of the Ukrainian Insurgent Army,” the UPA.

The partisan formation is seen in Ukraine as a symbol of heroic resistance against the Soviet forces in the fight for Ukrainian independence. In Poland, however, the UPA is notorious for killing up to 100,000 Poles in the Volhynia region between 1943 and 45, in an attempt to ensure the territory did not become part of postwar Poland.

The area has changed hands numerous times and now lies in Ukraine, after it suffered Soviet and then German Nazi occupation. In 2016, the Polish parliament unanimously adopted a motion calling the killings a “genocide committed by Ukrainian nationalists”.

Polish underground forces went on to kill 10,000 Ukrainians in reprisals, historians say. The episode remains one of the most painful and unresolved issues in bilateral relations between the countries.

Zelenskyy’s decision sparked anger in Poland and accusations of historical insensitivity, dampening hopes of a breakthrough after last year’s agreement on exhumations, in which Ukraine agreed to first steps that could ultimately allow Polish families to bury their massacred relatives.

The conservative President Karol Nawrocki – a former head of Poland’s Institute of National Remembrance – said he was “outraged” by Zelenskyy’s decision to name the unit after UPA, suggesting Zelenskyy could be stripped of Poland’s highest civilian honour, the Order of the White Eagle, which was conferred on him in 2023.

After weeks of frantic behind-the-scenes discussions between Warsaw and Kyiv, no compromise was found on the naming issue, with both sides trading blame for lack of progress. On Friday, Nawrocki confirmed he would be revoking the order from Zelenskyy.

“Ultimately, the position of the Ukrainian side did not change. History should not be an obstacle to the future, but a good future can only be built on truth,” he said.

“If anyone wants to be proud of the murderers of women and children, they cannot be surprised by the reaction,” Nawrocki’s chief foreign policy adviser, Marcin Przydacz, said.

A poll for the Polish media showed that a majority of Poles supported the move.

Over the weekend, Zelenskyy sent the award back by post and hit back at Nawrocki, alleging he sought to exploit rising anti-Ukrainian sentiments ahead of next year’s parliamentary election in Poland, drawing parallels with Hungary’s ousted prime minister, Viktor Orbán.

“Our service members ​choose a ‌heroic name for ​their unit themselves, ​and as president and supreme commander-in-chief, I must support them,” he said.

Zelenskyy also warned that the dispute would weaken Polish-Ukrainian relations at a time of rising tensions with Russia.

“Without Ukraine, no one will be able to defend Poland. It is simply impossible,” he said.

In a rare sign of unity across the political divide in Ukraine, his predecessors, Leonid Kuchma, Viktor Yushchenko and Petro Poroshenko, also sent their Polish honours back, as did several senior Ukrainian officials.

Zelenskyy’s snub will be embarrassing for Poland’s pro-European prime minister, Donald Tusk, who will be the main host of the conference in his home town of Gdańsk and who has repeatedly urged both presidents to de-escalate.

Tusk previously warned that an escalation between the two presidents would be “a strategic mistake that will cost both sides”.

Speaking before the cabinet meeting on Tuesday, Tusk said he was “very well aware” of the anti-Ukrainian sentiment, which he said was sometimes “justified”, but accused politicians in both countries of “stoking tensions rather than building solidarity and accord between Ukraine and Poland”.

“But keeping in mind the strategic security and interests of Poland … I will not lend a hand in any way to stoking these tensions,” he said.

Poland has been one of Ukraine’s closest allies since the full-scale invasion in 2022, becoming home to more than a million Ukrainians who fled in the first months of the war. It also remains a strategic logistics hub for deliveries to Ukraine.

Meanwhile, the EU warned on Tuesday that only Russia would benefit from worsening relations between the two neighbours, saying it hoped the conference – which will be attended by the commission president, Ursula von der Leyen – would still prove a success.

“There’s only one happy observer in this type of situation, and that’s the aggressor in Ukraine, and so we shouldn’t be playing into their hands,” EU spokesperson Paula Pinho said.