President Volodymyr Zelensky signed a decree granting the honorary title "Heroes of the UPA" to the Special Operations Forces' Independent Special Operations Centre "North".
He said the move was intended to "restore the historical traditions of the national military" and recognised the unit's exemplary performance in defending Ukraine's territorial integrity.
Poland's foreign ministry said it viewed the decision "unequivocally negatively", warning it "wounds the memory of the organisation's victims and strikes at the dialogue between our nations".
It also cautioned that the move could be exploited by Russian propaganda seeking to drive a wedge between the two allies and undermine international support for Ukraine.
The Institute of National Remembrance (IPN), Poland's state historical body, described the UPA as directly responsible for genocide against Poles in Volhynia and Eastern Galicia between 1943 and 1945, and said the glorification of the organisation "must provoke opposition from all those who remember its actions".
According to historians, in July 1943 the UPA carried out coordinated attacks on around 150 Polish villages across four districts of the Volhynia region – an event known in Poland as the Volhynia massacre.
The perpetrators were members of the Bandera faction of the Organisation of Ukrainian Nationalists (OUN-B) and the UPA forces under its command.
The two countries have long disagreed over how to characterise these events.
Poland considers them genocide; Ukraine has generally described them as the consequence of a mutual armed conflict for which both sides bore equal responsibility.
Ukrainians have also tended to view the OUN and UPA primarily as anti-Soviet organisations, given their postwar resistance to the USSR, rather than as anti-Polish ones.
The row comes days after Ukrainian authorities repatriated the remains of OUN leader Andriy Melnyk for reburial in a ceremony attended by Zelensky and senior Ukrainian officials.
Israel's Yad Vashem Holocaust memorial expressed serious reservations, saying the commemoration of a leader of a formation that collaborated with Nazi Germany undermined the memory of Holocaust victims.
(ał)
Source: PAP