An undercover television report that showed members of a Polish neo-Nazi group celebrating Adolf Hitler's birthday and burning a swastika has prompted a criminal investigation.

Poland's prime minister also denounced fascism in response to the report broadcast by Polish news channel TVN24 on Saturday.

The report featured members of a group called Pride and Modernity wearing Nazi uniforms. It said the same group was behind a November protest where pictures of centrist European Parliament lawmakers from Poland were hung on mock gallows.

Poland's prosecutor general opened an investigation Sunday for suspected "public propagation of fascism," a crime punishable by up to two years in prison.

Prime Minister Mateusz Morawiecki said propagating fascism tramples "the memory of our ancestors and their heroic fight for a Poland that is just and free from hatred."