The digital creatures, which appear overlaid on the real world as part of the hit smartphone game Pokémon Go, have been reported at the former concentration camp Auschwitz in Poland, the United States Holocaust Memorial Museum in Washington D.C. and the National September 11 Memorial in New York, provoking frustrated responses from the representatives of some of the sites.

A spokesman for the Auschwitz Memorial said that any presence of the game there, or at any other memorials and Holocaust museums, was “absolutely inappropriate.”

“Allowing such games to be active on the site of Auschwitz Memorial is disrespectful to the memory of the victims of the German Nazi concentration and extermination camp on many levels,” Pawel Sawicki said in an email.