Polish police have asked prosecutors to examine evidence against ultra-nationalists who demonstrated at Auschwitz on Holocaust Memorial Day.
Police sent them video of the group, estimated at 70-100, who marched with big Polish flags at the notorious Nazi death camp site on Sunday.
The protesters were led by Piotr Rybak, who was convicted in 2015 for publicly burning an effigy representing a Jew.
The Nazis murdered nearly 1m Jews and 150,000 non-Jewish Poles at Auschwitz.
The main commemoration at Auschwitz on Sunday involved Jewish survivors and Polish government officials.
About half of the Jews murdered in the Holocaust were Polish. There were many other victims of Nazi Germany at Auschwitz too, including Soviet prisoners-of-war and Gypsies (Roma).
The colossal death toll has been documented by the US Holocaust Memorial Museum, among others.
The ultra-nationalist march on Sunday took place away from the main commemoration at the site.
It is reported to be the first such protest at the site on one of the most solemn days for Jews worldwide.
Rybak, quoted by Reuters news agency, told his supporters: "The Jewish nation and Israel is doing everything to change the history of the Polish nation. Polish patriots cannot allow this."
Police said on Twitter that they had analysed material collected, "including recordings and photos from the assembly of Piotr Rybak", and sent the evidence to the district prosecutor's office.
They gave no details about the evidence collected.
Research shows that some Poles participated in the Holocaust, but many other Poles risked their lives to save Jews.