BERLIN (AP) — An activist group has apologized to Jewish organizations outraged over their use of purported Holocaust victims’ remains in an installation outside Germany’s parliament building meant to draw attention to the perils of far-right extremism.

The Center for Political Beauty, a Germany-based activist group known for provocative stunts, installed an urn outside the Reichtstag building on Monday, saying it contained victims’ remains that it had unearthed from 23 locations near Nazi death and concentration camps in Germany, Poland and Ukraine. Soil the group said contained the remains could be seen in the transparent orange urn, about the size of an oil drum, set atop a metal pillar.

Following the uproar from Jewish organizations decrying the stunt as an instrumentalization of the Holocaust and an affront to the dead, the group apologized and by Thursday morning the urn had been wrapped in opaque black plastic so its contents could not be seen.

“We want to apologize especially to Jewish institutions, associations and individuals who see our work as disturbing or touching the peace of the dead according to Jewish religious law,” the group said on its website in a post late Wednesday.

Six million European Jews were murdered by the Nazis, many of them transported from around Europe to be killed in death camps like Auschwitz, Sobibor and Treblinka that the Germans established in occupied Poland.

The activist group, whose members consider themselves political artists, had said the urn should serve as a warning in times of growing far-right extremism of how conservative forces in Germany helped pave the way for Adolf Hitler’s fascists to come to power in 1933.