A group of 11 people have been detained after stripping naked, slaughtering a sheep and chaining themselves together at the entrance to Auschwitz.
The men and women, who have not been identified, also draped a white banner with the word "love" in red lettering over the Nazi death camp's infamous Arbeit macht frei gate, according to local media.
The group used a drone to film the stunt.
Bartosz Bartyzel, a spokesman for the Auschwitz memorial, said their motives remained unclear.
He said museum guards ordered the group to dress and then called police to the camp near the southern Polish city of Oswiecim.
"We're shocked and outraged by this attempt to use the memorial site for a protest and which mars the memory of thousands of victims. It's a reprehensible act," he added.
A statement from the Auschwitz memorial authorities said that "using the symbols of Auschwitz for any manifestations or happenings is reprehensible and outrageous" and "hurts the memory of all victims" at the death camp.
Malgorzata Jurecka, a spokeswoman for local police, said those arrested were aged between 20 and 27 and were from Poland, Belarus and Germany.
They face allegations of desecrating a memorial site and if convicted could be landed with hefty fines.
Local media reported the group staged the incident as a protest against the conflict in Ukraine.
During the Second World War, the Nazis killed 1.1 million people at Auschwitz between 1940 and 1945, mostly Jews but also Poles, Roma and Russian prisoners of war.