Sikorski made the comments at a joint press conference with his French counterpart, Jean-Noël Barrot, when asked about the incident and wider strain in Polish-Ukrainian relations.
On 3 July, a group of men demanded entry to an office run by a Ukrainian businesswoman at Poznań University of Economics, saying they wanted to check whether she "supported Stepan Bandera" – a Ukrainian nationalist leader whose followers were responsible for the mass killing of Poles during the Second World War.
Footage of the encounter was shared online, with a caption describing the men as activists supporting Grzegorz Braun and Janusz Korwin-Mikke, two far-right Polish politicians.
The woman refused them access and told police she had been defamed.
Two men were detained on Wednesday over the incident.
Poland's Interior Minister, Marcin Kierwiński, said there was "no room for hatred and aggression" and that police would respond firmly to such cases.
Separately, private broadcaster Polsat News reported that one of those detained, a former Territorial Defence Force soldier, had already been arrested in March on suspicion of spying for Russia.
He was released without pretrial detention after a court ruled the evidence was insufficient at that stage.
It is the latest in a series of such incidents.
In June, Polish authorities took action against self-styled far-right vigilante patrols that had been stopping and questioning foreigners near Warsaw's central railway station, condemning the groups as illegal and accusing them of unlawfully impersonating police officers.
Officials said the patrols had caused fear and psychological distress among residents and visitors; police seized evidence at several locations and reinforced security around the station.
Speaking on Thursday, Sikorski said anyone wishing to check people's identities in Poland should apply to join the police, municipal or border guard instead, calling such actions illegal.
He appealed directly to "sponsors" of radical militias not to stoke "tribal emotions."
The minister linked the Poznań incident to a wider row over history between Warsaw and Kyiv, which intensified after President Volodymyr Zelensky decided in late May to name a military unit after the Ukrainian Insurgent Army (UPA), a nationalist force blamed for the wartime killings of Poles.
Sikorski warned the issue risked fuelling dangerous sentiment among Ukrainians in Poland and the Polish minority in Ukraine.
He noted that the tension had been welcomed publicly by former Russian President Dmitry Medvedev and a Kremlin spokeswoman, adding that in any rivalry between Warsaw, Kyiv and Moscow, "it is always Russia that benefits."
Poland and Ukraine are set to mark the anniversary of the 1943 Volhynia massacre, in which Ukrainian nationalists killed tens of thousands of Poles, on 11 July.
A ministry spokesman also warned that impostors posing as officials could try to stir up hostility between the two countries in the coming days, urging the public to stay alert to potential Russian provocation.
(ał)
Source: PAP, polsatnews.pl