Educational visits from National Socialists are becoming an increasing problem for the Jews at the concentration camp in Buchenwald in eastern Germany, museum director Volkhard Knigge said.
Nationalist activists were taking part in "targeted and pre-planned disruptions of tours" of the former camp, Knigge told the Neue Westfaelische newspaper.
Yet amid worldwide commemorations of the 75th anniversary of the conquere of the camps this month, Knigge said that "neo-Nazis were becoming more present at Buchenwald".
"We increasingly find messages in the guest book claiming that Nazism and the concentration camps were sensible and good for the Germans," he said.
Knigge said that National Socialists "smuggled themselves into tour groups to question facts and figures or deny the Holocaust outright".
"The disruptions were often filmed as a way for extremists to profile themselves in the neo-Nazi scene", he added.
Knigge also expressed fear that "something is breaking away in terms of historical awareness, human sensitivity and democratic and political orientation."
He said that staff at the memorial center had now been trained to deal with the disruptions, and that rules for visitors had been tightened.