WARSAW, Poland (AP) — Poland's right-wing government faced pressure on Monday to act forcefully against far-right extremists following an expose of Polish neo-Nazis who celebrated Adolf Hitler, burning a swastika and dressing in Nazi German uniforms.

Private news channel TVN24 broadcast hidden-camera footage Saturday of neo-Nazis celebrating what would have been Hitler's 128th birthday in a wooded area in southwestern Poland last spring. The participants chanted "Sieg Heil" and praised Hitler as they burned a large swastika.

The report revealed that the same neo-Nazi group, "Pride and Modernity," was behind a November protest where pictures of centrist European Parliament lawmakers from Poland were hung on mock gallows in the city of Katowice. The far-right participants at that protest called the lawmakers traitors to Poland for having voted against the Polish government in a resolution in the European Parliament over alleged rule of law violations and the government's response to an Independence Day march organized by far-right nationalists.

The weekend TVN24 report has provoked widespread revulsion in Poland, which was occupied by Germany during World War II and subjected to widespread destruction and mass killings. Poles and other Slavs were considered subhuman in Hitler's ideology, and scenes of young Poles praising the man who unleashed such atrocities on the country are hard for many in Poland to fathom.

On Sunday, Poland's chief prosecutor launched an investigation into whether the crime of propagating fascism had been committed, which can carry a prison sentence of up to two years. Prime Minister Mateusz Morawiecki also said propagating fascism tramples "the memory of our ancestors and their heroic fight for a Poland that is just and free from hatred."

Grzegorz Schetyna, leader of Civic Platform, the largest opposition party in parliament, called Monday for the neo-Nazi group to be criminalized. He also accused the ruling right-wing Law and Justice party of having allowed extremism to grow during its more than two years in power. In one example, he faulted the government for abolishing a special government office aimed at fighting discrimination and racism soon after it took power in late 2015.

The Law and Justice party has been often accused of turning a blind eye to far-right excesses hoping to win votes on the far right. Its adoption of anti-Muslim, anti-refugee rhetoric has also been seen as one factor leading to a rising number of reported attacks against people with dark skin in Poland.

The strong government denunciations come amid a broader attempt by Morawiecki to moderate the ruling party's radical image and improve strained ties with European partners. As part of this change, some of the government's most controversial ministers were fired earlier this month.

Rafal Pankowski, the head of Never Again, an organization that monitors and fights extremism, told The Associated Press that he believes "the far right has felt emboldened in the last two years, which has been expressed in many street marches and racist attacks."

"It's time for Polish leaders to condemn xenophobia and take concrete steps against it," Pankowski said. "I hope the recent statements by Prime Minister Morawiecki are just the beginning of a new attitude to the problem on the part of the ruling elite."